Abstract: A portable length probe having a length measuring wheel with light transmission holes at equally spaced angular intervals thereon, which wheel is rotatably mounted in an integral one piece nose body having a photo-responsive element and a light-emitting element disposed in aligned facing relation in a common bore formed in the nose body transverse to the wheel. The photo-responsive element is an infrared sensitive photo-transistor and the light emitting element is an infrared light emitting diode (LED), and both are encased in cylindrical opaque cases which fit in generally complementary sliding relation within the bore, the cases each having an optically open end facing one another. Increased accuracy is provided by employing frequency doubler circuitry in conjunction with the wheel, in which the wheel light transmission holes are substantially uniform in angular width and are spaced apart a distance substantially equal to such hole angular width.

Abstract: A portable hand-held length probe with a length measuring wheel and a tracing unit which is mounted adjacent the wheel and is movable by pressing the tracing unit against a surface to be measured. A wheel movement indicative output signal is effected as function of wheel movement, and the probe carries a switch which is actuated as a function of depress-release movement of the tracing unit to enable or disable transmission of the wheel movement indicative output signal.

Abstract: A hand-held portable length probe having a length measuring wheel and a tracing unit disposed adjacent the measuring wheel, the tracing unit being slidably carried by the probe housing and acting to actuate a switch secured in fixed relation on the probe housing. The switch is illustrated as a miniature snap action switch, actuated by the slidable tracing unit either directly or indirectly through an intermediate adjustable spring lever arm; and is also illustrated as a magnetically actuated switch in the form of a reed switch which is actuated by a permanent magnet carried by the sliding tracing unit. The wheel is carried in a removable nose element which serves to aid in anchoring the tracing unit housing to the length probe main housing. The switch is carried, in the illustrative examples, by a retention clip.