Martin Brenner's, Pilot Balloon Resources
Warren-Knight Model 8403 Pibal Theodolite
The Warren Knight model 20-8403 is the current production model of a series of theodolites meeting the Military Specification ML-47 and ML-474. This model is derived from the David White 6061 machines dating back to the 1940's. Production tooling was purchased from David White in the early 1960's at which time production ceased at David White and resumed at Warren Knight. Early Warren-Knight production units were identical to David White 6061 units. Even the part numbers were the same containing the numbers 6061 in them. The current Warren Knight 20-8403 instrument has some refinements over the 6061 instruments yet many of the parts are the same and with the exception of the detachable battery box operationally they are unchanged for the 65+ years the ML-47 specification instruments have been in existence.
Construction materials, the battery box and paint colors differ from David White units and earlier Warren Knight Model 84 and 474 Theodolites. (the battery box on the 20-8403 is the black tubular housing on attached to the far side standard with the shiny aluminum cap.) Seiler of St. Louis MO. made a small number of ML-47 specification instruments. They are operationally identical to David White 6061 and early Warren-Knight instruments. However they were not produced with the same tooling so they are a bit different.
The 20-8403 and models from which it has descended have the following features:
Bent Axis telescope, 21 power 42mm main objective with 4 power 17mm wide angle objective finder scope. Both objectives are sighted through the same eyepiece. Gun site, two pair, one fixed, one folding (hinged), mounted on the telescope. These theodolites utilize circles divided into degrees with 10ths of a degree directly read from micrometer drums that are positively engaged into the circles by tangent screws. The circles and reticule (cross hair - spider web) are lit by 3 volt lamps the reticule is dimmed by a rheostat. A compass is permanently attached.
Variants are also produced: Model 85 (20-85xx) Shore type - 6.3 volt lamps, no compass. Model 83 (20-83xx series) for telemetering, as well as other options variations including an inverting prism.