Abstract: A circular target type bubble level slides easily onto and off of a standard surveyor's sight rod. When slid into position at any desired elevation on the rod for optimal viewing and released, the device automatically assumes a position such that the indicating plane of the level is exactly at right angles to the long axis of the rod. When the rod is adjusted so that the bubble level indicates the true horizontal, then the rod will be plumb. The rod is received in a through hole of a rod-encircling member. A spring bias element within the hole is forced against the rod. This forces a diametrally opposed support wall portion of the member against the rod with sufficient force to hold the level at any position on the rod without operator adjustment. It also automatically positions the indicating plane of the level orthogonal to the long axis of the rod, because the bubble level element is rigidly mounted with the desired orientation relative to the support wall portion forced against the rod.

Abstract: An instrument and method for measuring the invert of a sewer pipe relative to a manhole employs a horizontal bar which spans the manhole and rests upon its rim. A sight rod is slideably mounted on a sleeve fixed to the bar. The sleeve has adjustments for mounting the bar in true vertical and plumb position with a spirit level. Removably connected to the lower end of the rod is an arm which extends laterally and below the rod at its distal end. The rod is lowered until the distal end of the arm contacts the invert of the pipe. The vertical distance between the bottom of the arm at contact with the invert and the intersection of the rod with the bottom of the horizontal bar yields the desired elevation. It may be read directly off the sight rod when the rod is specially marked with corrected graduations.