Abstract: A tilt predictor incorporated into a total station to predict the degree of tilt of the rotational alidade portion of a total station corresponding to the rotational orientation of the rotational alidade portion. In one embodiment, the present invention defines the plane of rotation for the rotational alidade portion with the rotational alidade portion disposed in a first rotational orientation. The rotational alidade portion is then rotated to the desired rotational orientation. This embodiment then predicts the degree of tilt of the rotational alidade portion at the desired rotational orientation.

Abstract: An audible signal generator incorporated into a total station to audibly indicate to the user the rotational orientation of the total station, and a method for using the audible indication to perform the tilt sensor calibration. In one embodiment, the present invention indicates to the user of the total station when the tilt sensor has been calibrated with the total station in a first rotational orientation. This embodiment then audibly indicates to the user when the rotational alidade portion of the total station has been rotated to a second rotational orientation. This embodiment then audibly indicates to the user when the tilt sensor has been calibrated with the total station in the second rotational orientation.

Abstract: An automatic optical plumbing instrument includes: an objective telescopically mounted at a front portion of a telescopic housing adjacent to an object to be observed, an ocular telescopically mounted at a rear portion of the housing adjacent to an observer's eye, and a transparent plumbing protractor defining a plumbing line thereon and mounted in the housing between the objective and the ocular, whereby upon entrance of a vertical line (or plane) of the object into the instrument to form an image therein, a verticality of the vertical line (or plane) of the object can be checked whether the vertical line is aligned with the plumbing line marked on the protractor, thereby providing a plumbing instrument for calibrating a verticality of the object.

Abstract: A constructional laser having a light source (5) for emitting a laser beam (L) arranged in housing (2) and rotatable about a rotational axis (A), a motor-driven shaft (14) supported in the housing (2) for rotation about the rotational axis (A) and having an end projecting into a casing (3) at least partially projecting above the housing (2) and having at least one beam hole (7, 8), with the shaft (4) being rotationally connected with the casing (3), and a direction-changing device (9) for the laser beam (L) and supported on the end of the shaft (4) projecting into the casing (3), with the casing (3) having a peripheral wall (33) spaced from the direction-changing device (9) and with the casing being capable of a limited displacement relative to the housing (2), without any contact between the peripheral wall (33) and the direction-changing device (9).

Abstract: An instrument for use in alignment, plumb and leveling functions includes a laser diode projecting a beam through a liquid contained in a vessel. Floating in the liquid is a compensator float which includes telescope optics so as to diminish the angle of rays leaving the telescope as compared to rays entering the telescope. The laser beam passes through the liquid and through the telescope, exiting from a window at the top or side of the instrument. By selecting the proper relationship between the telescope's magnification and the index of refraction of the liquid, the instrument is made to correct for small tilt angles of its housing. Various embodiments are disclosed for projecting upward or downward plumb beams, level beams or both.

Abstract: A laser transmitter includes an optical system arranged to generate laser beam and configured to project the laser beam radially so as to define a plane through which the laser beam is projected. A positioning device is coupled to the laser transmitter for adjusting an angular orientation of the optical system with respect to a first axis and with respect to a second axis. The angular orientation of the laser transmitter is adjusted so that the plane through which the laser beam is projected has a first slope with respect to the first axis and a second slope with respect to the second axis. A rotary encoder is arranged to determine a rotary position of the laser beam as it rotates to define the plane. A target is positioned in an alignment direction corresponding to the direction to which the laser transmitter is to be aligned. The laser transmitter may be aligned with respect to the first axis, the second axis or some other reference.

Abstract: A low cost automatic laser level instrument uses a solid laser diode module as the laser source. It is not necessary to adjust the laser diode module to make the center ray align with the concentric axis. The only requirement is adjusting a reflecting mirror or prism so that the center ray is vertical to the rotating axis. In other words, any ordinary diode module can be used. The device levels automatically by means of a pendulum. The pendulum remains steady under the influence of a magnetic field. The magnetic field functions as a damper, which stops the swinging of the pendulum very quickly. After adjusting the center ray to be perpendicular to the pendulum (which points to the earth's core), the device will produce a standard level line.

Abstract: A tool resembling a carpenter's level is used in establishing a precise level line and projecting an existing line using a visible laser beam projector in the same instrument. A manual selector device is provided for switching from a laser beam parallel to a reference surface to one which self-levels in one axis. Methods for switching between modes are described as well as a tilt compensator.

Abstract: An apparatus for displaying a direction for adjusting its height to its appropriate height includes a plurality of light sources, a light receiving portion, and a control unit. The light sources are arranged in the form of a matrix in a display portion of the apparatus and displays the direction as a moving shape by emitting light in turn. The light receiving portion receives an incident beam and outputs a signal corresponding to a height of the incident beam. The control unit controls the light emission of the light sources in accordance with the signal so as to move the shape downward or upward to indicate the appropriate height. The control unit controls the light emission of the light sources so that at least one light source of a group of the light sources is lighted after a predetermined time, shorter than a time during which a human eye can keep an afterimage, after other members of the group were lighted.

Abstract: A low cost automatic laser level instrument uses a solid laser diode module as the laser source. It is not necessary to adjust the laser diode module to make the center ray align with the concentric axis. The only requirement is adjusting a reflecting mirror or prism so that the center ray is vertical to the rotating axis. In other words, any ordinary diode module can be used. The device levels automatically by using a knife edge that is propped up by a universal ring. The pendulum remains steady under the influence of a magnetic field. The magnetic field functions as a damper, which stops the swinging of the pendulum very quickly. After adjusting the center ray to be perpendicular to the pendulum (which points to the earth's core), the device will produce a standard level line.

Abstract: The present invention provides a laser leveling system for forming a reference line or a reference plane by a laser beam. The laser leveling system comprises a laser light emitting means for emitting a laser beam, a projection optical system for projecting the laser beam irradiated from the light emitting means, a rotating unit for rotating the light beam projected by the projection optical system, and a leveling means for tilting the rotating unit, whereby a horizontal reference plane and a vertical reference plane are formed by the light beam, and a reference irradiation spot is formed on the horizontal reference plane or on the vertical reference plane.

Abstract: Accessories are disclosed for use with a laser tool which may or may not be self-leveling. The accessories include one or more diffraction elements, effective to receive the incoming beam and produce a plane of diverging laser beams. In preferred embodiments the diffraction elements are self-leveling. When the diverging beams are directed against a surface such as a floor, wall or ceiling, a series of discrete spots define a visible reference line useful in construction layout. The spots themselves may each locate the position of a fastener to be installed, for example, by giving the approximately correct spacing for reference of the user. The generation of discrete spots rather than a solid line, as would be generated by a cylindrical lens, better allocates laser power by providing brighter, more visible reference elements on the wall or ceiling.

Abstract: A self-aligning laser transmitter having a dual slope grade mechanism is provided. The laser transmitter includes a light source coupled to a frame which is suspended from a gimbal mechanism. The gimbal mechanism and the frame are coupled to a rotatable base. X and Y axes leveling devices are coupled to the gimbal mechanism and the frame to level the light source. A grade arm having two level sensors mounted at ninety degrees to one another is coupled to the frame. The grade arm is pivoted along the X or Y axes by a grade arm pivoting device. The X and Y axes leveling devices reposition the light source so that the level sensors are level thereby introducing a slope to the light source corresponding to the amount of pivot of the grade arm. The base may be rotated for a dual slope capability. The laser transmitter may be self-aligned automatically by aligning the laser transmitter with a target positioned at a reference location.

Abstract: A laser gradient setting device, having such arrangement that a reference laser beam with a gradient emitted and a reference laser beam in vertical direction is emitted, whereby the laser gradient setting device can be easily positioned by the reference laser beam in vertical direction by a single worker.

Abstract: A device for projecting a flat beam of diverging laser rays comprises a base supporting a movable gravity self-leveling equipment and at least a laser beam or ray projector mounted thereon and provided with an optical lens assembly for transforming the laser beam emitted by the projector into a flat beam of diverging laser rays and laying in a horizontal or vertical plane for projecting at least a straight line laying on a perfectly horizontal or vertical plane.

Abstract: In a horizontal position error correction mechanism for an electronic level according to the present invention, a collimation optical system collimates a level rod, and a calculation processing device processes an output signal of a photoelectric converter by calculation to calculate a difference of elevation and so forth. A compensator device formed on a telescope optical system for maintaining a horizontal position corrects an inclination of the electronic level to maintain the horizontal position of the electronic level, and a suspended optical member suspended from the compensator device is rocked in forward and backward directions and leftward and rightward directions in response to an inclination of the compensator device.

Abstract: The present invention relates to a laser beam levelling device which has a rotating frame which is rotatable round a vertical axis and an inclining arrangement which is pivotal round a horizontal axis. Means connected to a controller are also provided to enable the rotated and inclined position to be monitored. One inclining arrangement can be orientated and inclined by the controller such that the laser plane formed by a rotating laser beam is inclined in a specific direction by a specific angle. This inclination is an auxiliary inclination by means of which the laser plane is simultaneously inclined in a longitudinal and transverse gradient differing from this auxiliary direction of inclination in each case. The auxiliary direction and the auxiliary inclination are calculated automatically by the controller on the basis of the desired longitudinal and transverse gradient of the laser plane and are converted into corresponding control commands.

Abstract: The projector device for laser rays (4) is mounted on an apparatus which oscillates and is self-leveling (2, 3, 5) under the force of gravity whereby in the equilibrium position a ray is projected on one or more walls always in a perfectly horizontal position. The oscillating apparatus is interrupted in its oscillations by a manual mechanical brake (6, 7, 8 and 9). The device can rotate and includes a graduated ringnut (11) on which it is possible to read the angle of rotation of the laser ray with respect to a predetermined reference point.

Abstract: A number of embodiments of targets, for use with scanning light beam leveling/marking devices, are constructed with their elements incorporated as target structure. The lens and beam divider functions are formed into optical quality parts such as a polycarbonate block, these parts thus are made essentially as an integral element, or the function of those elements can be provided by a first hologram which is optically equivalent of the input lens and beam dividing axicon, and the viewing screen diffuser function provided by a second hologram, and these holograms may be made on a single substrate, to improve and maintain alignment. The optical path for the impinging light beam (after it is divided) may be transmitted and reflected from the input to the view window through one or more reflector surfaces, with the body of the target functioning as a waveguide.

Abstract: A self-levelling laser generator apparatus (10) includes a housing (12), a light source in the housing which produces a beam of collimated light, and a self-levelling mechanism (18). The self-levelling mechanism includes an electronically controllable signal source, such as a digital potentiometer (46), which is provided a command (44a-44c) from a programmed computer (38) to produce a controllable output (48). The output of (48) the digital potentiometer is summed by a summing circuit (34) with the output (28) of an inclination sensor (24) in order to produce a compensated inclination signal (36) which is provided as an input to computer 38. The computer additionally receives a calibration input (20, 21) indicative of deviation between the inclination of the laser beam and a predetermined grade. The computer produces a drive signal (50a, 50b) for the self-levelling mechanism (52, 54) that is a function of the compensation inclination signal.

Abstract: A self-adjusting level for determining the leveling between two distant points is disclosed. It mainly contains a main body and a light beam indicator. The main body contains a flame having two oppositely disposed supporting arms, a disc-like base disposed below said main body, and a 360-degree rotatable graduated angle-measuring disc disposed between said base and said frame.

Abstract: A laser gradient setting device, which comprises a swing frame rotatable around a vertical shaft, a laser projector tiltably mounted on the swing frame via a support member so that it is tiltable around a horizontal shaft, a tilt sensor mounted independently from the laser projector and rotatably around the horizontal shaft, an encoder integrally rotating with the tilt sensor, a vertical angle adjusting means for tilting the support member, and a tilt sensor tilting means mounted on the support member and for tilting the tilt sensor, whereby the tilt sensor is tilted so that the tilt angle detected by the encoder agrees with the preset gradient and the tilt sensor is integrally tilted with the laser projector so that the tilt sensor is held horizontally.

Abstract: According to the present invention, fixed tilt detectors are fixed in planes crossing perpendicularly to each other of shaft center of a laser projector, and tilting tilt detectors are mounted on a plate, which is tiltable with respect to shaft center of the laser projector. The laser projector is leveled in such manner that the fixed tilt detectors indicate horizontal direction or tilting tilt detectors aligned with the fixed tilt detectors indicate horizontal direction, and horizontal reference plane is obtained. The tilting tilt detectors are tilted with the fixed tilt detectors as reference, and the laser projector is leveled so that the tilted tilting tilt detectors indicate horizontal direction, and reference plane tilted at an arbitrary angle is obtained.

Abstract: An automatic plumb, level and pointing tool uses a visible laser diode to project light beams in two modes through two windows. In the first mode of operation, the unit is able to project a plumb-up beam and a level beam of light while resting on a surface which is as much as 5.degree. out of level. In the second mode of operation the unit is able to project two orthogonal beams or light both approximately in the horizontal plane for aligning one or more reference lines. Accurate, low cost methods of generating level and plumb beams and planes of light are disclosed. One method uses an approximately or partially leveled platform combined with a refractive correction as a second stage.

Abstract: A laser gradient setting device, having such an arrangement that a reference laser beam with a gradient is emitted and a reference laser beam in vertical direction is emitted, whereby the laser gradient setting device can be easily positioned by the reference laser beam in vertical direction by a single worker.

Abstract: An apparatus for setting a level plane includes a spirit level having a parallelepiped shaped housing with a measuring base and a leveling plate with an upper plate surface on which the base of the housing of the level is disposed. The upper plate of the leveling plate may be tilt orientation adjusted with respect to a lower plate that is spaced away from the upper plate by adjustment screws between the upper and lower plates. The upper plate includes a ferromagnetic material and a pivot pin projecting up from it. The spirit level housing has a hole in which the pivot pin is disposed enabling the housing to be pivoted around the surface of upper plate. A retaining magnet in the housing in the region of the measuring base holds the housing to the upper plate. Alternatively, the spirit level housing has the ferromagnetic material while the magnet is in the upper plate. Alternatively, also, the housing includes the pin while the hole is in the upper plate.

Abstract: This invention provides a laser beam transmitting apparatus which can make the levelling work unnecessary to thereby mitigate the burden of an operator and improve work efficiency. The apparatus is provided with a base, a beam transmitter for supplying a beam of light, a housing, for holding the beam transmitter, and a levelling mechanism provided between the housing and the base, the housing being oscillatably supported on the base, and the center of oscillatory movement thereof lying above the centroid of the housing. Thus, there is achieved double bearing combined with a precise levelling mechanism, provided between the beam transmitter and the housing.

Abstract: A self-leveling plumb, level and pointing tool uses a visible laser diode to project light beams in two modes through two windows. Accurate, low cost structures for generating level and plumb beams and planes of light are disclosed. In principal embodiments, all leveling is accomplished using a very flexible coil spring as a pendulum element, a chain link connection in combination with such a spring, or a point contact suspension. Several accessories are disclosed for use with the laser tool, as well as other embodiments.

Abstract: According to the present invention, fixed tilt detectors are fixed in planes crossing perpendicularly to each other of shaft center of a laser projector, and tilting tilt detectors are mounted on a plate, which is tiltable with respect to shaft center of the laser projector. The laser projector is leveled in such manner that the fixed tilt detectors indicate horizontal direction or tilting tilt detectors aligned with the fixed tilt detectors indicate horizontal direction, and horizontal reference plane is obtained. The tilting tilt detectors are tilted with the fixed tilt detectors as reference, and the laser projector is leveled so that the tilted tilting tilt detectors indicate horizontal direction, and reference plane tilted at an arbitrary angle is obtained.

Abstract: An automatic plumb, level and pointing tool uses a visible laser diode to project light beams in two modes through two windows. In the first mode of operation, the unit is able to project a plumb-up beam and a level beam of light while resting on a surface which is as much as five degrees out of level. In the second mode of operation the unit is able to project two orthogonal beams of light both approximately in the horizontal plane for aligning one or more reference lines. An accurate, low cost method of generating level and plumb beams and planes of light is disclosed. One method uses an approximately leveled platform combined with a weak optical correction. The approximate leveling is done using a single wire or coil spring pendulum element which allows the platform to level itself to within a small fraction of true level, and remaining correction is provided by a weak negative lens or a weak reverse telescope.

Abstract: An apparatus for maintaining a scientific or measuring instrument or the like in a level horizontal plane. The apparatus comprises an inclinometer comprising a support housing and a plumb member freely suspended within the support housing. The plumb member has an exterior surface provided with first sensing means and the support housing has an interior surface provided with second sensing means cooperative with the first sensing means in determining simply variation of the support housing from an exact upright position. Automatic adjustment means are also provided which are responsive to the first and second sensing means for adjusting the support housing to maintain an upright positioning of the support housing and the instrument attached thereto.

Abstract: Various devices are disclosed for projecting a beam of coherent collimated light at a surface for use as reference lines and planes. The devices are also useful for projecting tracings of light in any of various geometric patterns. The devices comprise a pointer unit containing a light source, such as a laser diode. The light source is mounted so as to undergo periodic reciprocating motion in least one dimension, as imparted by any of various possible mechanisms. Combinations of such motions in two dimensions allows production of an infinite variety of geometric tracings. The pointer unit can be detachably mounted perpendicularly to a rotatable shaft provided by a base portion, or used separately as a level or hand-held pointer.

Abstract: An arrangement for one-man surveying, including a measuring station (1) and a target unit (2). A sighting-marker arrangement is provided which can be indicated by an indicator arrangement (7) on the measuring station. The measuring station (1) automatically takes a target seeking mode when the indicator arrangement (7) does not indicate the sighting-marker arrangement and a target following mode, when the indicator arrangement indicates the sighting-marker arrangement. The sighting-marker arrangement includes a combination of a first and a second sighting-marker unit. The first unit has a light source (8) on the target unit (2). The second unit has a light source (9) on the measuring station (1) and a reflector (11) on the target unit (2).

Abstract: A plumb device includes a direction determination unit suspended on an upper, movable, convexed portion of a universal joint. A lower, fixed, concaved portion of the movable joint is rigidly connected to a stand by means of a housing. The lower joint part has a lubricant supply line through which a lubricant can be introduced to a groove located on the upper joint part and positioned so as to be between the upper and lower joint parts.

Abstract: The article of which the verticality is critical, for example a distillation column disposed in a closed envelope, is associated with an indicator of verticality comprising a suspended mass and a locating ring. The envelope, which contains the various inner articles, is placed on a base by means of supports and its inclination with respect to the base is adjusted by controlling the relative position of the mass with respect to the ring. Application for example to cold boxes for the in situ production of gas from air.

Abstract: The present invention relates to projected light plumb device generally utilized in vertically aligning a floor position with a corresponding ceiling position in which a light projecting device is buoyantly supported within a fluid filled container. The light projecting device is selectively mounted on a float platform which is horizontally supported by the fluid in such a manner that regardless of the floor's inclination, the light projecting device will transmit a beam of light along a perfectly vertical line.

Abstract: A simple structure for providing a level laser beam. A pendulum is suspended by at least two suspension supports along the line parallel to a path of a laser beam emitted from a laser. An optical element is mounted on the pendulum to intercept the laser beam and reflect it along a path orthogonal to the first path. The pendulum will maintain the optical element in a vertical alignment, and accordingly the beam reflected off the optical element will be horizontal.

Abstract: A pendulous compensator for use in a light beam projector including a light beam source comprises first and second upper pulleys spaced from one another and secured to the light beam projector. First and second lower pulleys are positioned beneath the first and second upper pulleys and supported by filament strands, tapes, loops or the like extending around the upper and lower pulleys. A pendulum mirror is secured to and supported between the first and second lower pulleys for receiving a light beam from the light beam source and reflecting the light beam in a desired angular orientation relative to horizontal. The first and second lower pulleys in the pendulum mirror are supported such that the pendulum mirror is moved to compensate for tilting of the light beam projector. The first and second upper pulleys or a folding mirror may be controlled to select a grade angle relative to horizontal of a projected light beam.

Abstract: An apparatus is set forth for providing vertical alignment and indication of a fixture positioning within a dwelling relative to a floor plan reference point, wherein the apparatus includes a laser oscillator mounted within a lower first housing coaxially aligned through a second and third upper coaxially aligned housing to focus a laser beam onto the ceiling surface of the associated dwelling. A spherical housing is provided medially of the coaxially aligned first and second housings and includes support members for positioning of the housing upon a support surface, such as a floor, or optionally utilizes ring members and associated tether lines to suspend the organization relative to vertical support surfaces.

Abstract: The laser beam level instrument includes a laser diode mounted on a pendulous platform suspended from a frame by gold plated Mylar strips which also serve as conductors for supplying power to the diode. The strips are mounted with a 180 degree twist to overcome resistance to flexing/bending so that the platform moves freely under the influence of gravity to provide automatic self-leveling. The diode operates on low d.c. voltage but if d.c. is applied to the strips the magnetic field around the Mylar strips will have sufficient force relative to the geomagnetic field to interfere with free pendulation. So 4.5 volts d.c. is stepped up and inverted to about 20 volts a.c. to avoid interference with the geomagnetic field and to reduce power loss across the gold plated strips. The a.c. voltage is then stepped down and converted back to d.c. voltage (2-3 volts) on the platform to power the diode.

Abstract: A collimator solid state laser light source is spun at a very high speed to generate a reference plane for use in the construction industry. The drive housing and the laser light source are extremely compact, light and portable, and can be mounted to a surveyor's transit and telescope. Within the housing is a drive shaft which has the laser light source attached at precisely 90 degrees to the spin axis of the drive shaft. A logic circuit is also attached to the drive shaft so that the logic circuit board, the drive shaft, and the laser light source are all rotated as a unit. An electric motor and a motor control board card are positioned within the housing for rotating the drive shaft. The operator first calibrates the transit so that it is horizontal and positioned in plumb above the reference point.

Abstract: The present invention provides an inclinometer comprising a supporting housing and a plumb member suspended within that supporting housing. The plumb member is provided on its exterior surface with a sensor, while the supporting housing is provided on its interior surface with a sensor co-operative with the sensor on the plumb member for determining exact upright positioning of the supporting housing. The inclinometer, as arranged above, is useable in many different apparatus, including an apparatus for maintaining a scientific and measuring instrument on a level plane.

Abstract: A level sensor usable in a vehicle leveling and stabilizing apparatus particularly adapted for use with a motor home to level and stabilize the vehicle upon irregular terrain preparatory to camping or such activity. The apparatus includes a plurality of jack stand assemblies, one associated with each vehicle quadrant. Level sensors are connected to the motor vehicle to indicate level or off-level condition from front to rear and from side to side. A control panel within the vehicle carries the power unit controls and level indicators lamps. The level sensor includes a plate like pendulum suspended within a housing and constrained for back and forth pivotal movement in a fixed path. Electrical contacts are disposed on either side of the pendulum for making or breaking an electrical circuit responsive to pivotal movement of a pendulum as occurs when the housing is placed in an off level condition.

Abstract: A laser beam levelling instrument has a pipe length which is vertically and centrally mounted in the cover of a casing. The ends of this pipe length are pivotable, so that it can always be held in the vertical position. For this purpose two spirit levels are arranged at right angles to one another on a plate fixed to the lower end of the pipe length. The fluid in these levels is electrically conducting and the levels have electric contact points for operating a respective electric motor. The electric motors are provided with eccentric shafts which come into contact with the circumferential surface of the pipe length. If the pipe length diverges from the vertical, then the current from batteries ensures that it is brought back into the vertical position by means of the eccentric shafts. A laser light source is located in the lower part of the pipe length and a further pipe length is inserted in the upper end of the pipe length and can be rotated by a third electric motor.

Abstract: A surveying instrument and procedure are provided for the precise determination of elevation differences in the course of a surveying traverse. The instrument comprises an optical wedge 13 situated on the horizontal longitudinal line of sight axis 27 of the primary optical system between the objective lens 11 and a target under observation. The wedge is arranged for rotation about this axis and with such rotation angularly displaces the diverted line of sight 28 from the horizontal to the plane of the target. The degree of rotation required of the wedge to acquire the target 33 is measured by electro-optical angle encoder means 10, and the distance to the target by EDM means 24, 26. The difference in elevation is calculated trigonometrically by computer means utilizing as data the wedge diversion angle, the sine function of its rotation, the computed angular displacement of the line of sight, and the distance to the target.

Abstract: A self-leveling instrument mount comprises an instrument table pivotally mounted above a stationary frame on first, second and third vertical support arms. The first support arm is a fixed length member connected to the frame through a ball and socket joint. The second and third support arms are formed of screws extending between the table and frame having effective lengths that are controlled, respectively, by first and second servo motors in response to a pendulum switch to maintain the table parallel to a horizontal reference plane. The pendulum is magnetically damped during operation of the servo motors for stabilization. A mercury switch on the table disables the servo motors when the tilt of the table is too large to be leveled by the support screws.

Abstract: A self-leveling instrument mount comprises an instrument table pivotally mounted above a stationary frame on first, second and third vertical support arms. The first support arm is a fixed length member connected to the frame through a ball and socket joint. The second and third support arms are formed of screws extending between the table and frame having effective lengths that are controlled, respectively, by first and second servo motors in response to a pendulum switch to maintain the table parallel to a horizontal reference plane. The pendulum is magnetically damped during operation of the servo motors for stabilization. A mercury switch on the table disables the servo motors when the tilt of the table is too large to be leveled by the support screws.

Abstract: The optical sighting instrument uses the image of a floating bubble in a spirit level as a self-compensating index mark to indicate a reference line of sight at a given angle to the earth's normal surface.

Abstract: Transmitters generating rotating laser beams are commonly employed for surveying and earth working equipment control purposes. This invention relates to a method and apparatus for automatically maintaining the rotating laser beam in a required plane which is either exactly horizontal or at a known angle to the horizontal. The apparatus includes two remotely located laser beam reflectors which, when traversed by the rotating laser beam, respectively reflect the beam back to the transmitter along a path parallel to, but vertically displaced from the original path of the beam from the transmitter. Receiving equipment at the transmitter analyzes the vertical positions of the two reflected beams and effects any required correction of the position of the transmitter to maintain the rotating laser beam in the desired plane.