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David White Model 6061 Pibal Theodolite
This is a photo scanned from a meteorology text from the 1940's. Photos below show a similar theodolite that was manufactured for the US Army Signal Corps in 1941. This theodolite photographed below is marked ML-47-R also part of the ML-474 US military specification for a meteorological - aerological theodolite.
Some early units are made predominantly with brass parts while slightly later units (1943) contain major assemblies manufactured out of aluminum. Also note that the unit in the annotated photo unit lacks a finder telescope. It is possible that finder scopes were not made during these early years but retro-fitted later. I do not see them in early photographs and illustrations. I have 2, 6061 theodolites. One is fitted with a finder scope. This is not a simple addition as the eyepiece tube is different on finder scope equipped instruments. A parts manual dating from 1942 lacks finder scopes in the parts and drawings while a 1955 manual contains parts drawings with both configurations.
Early units utilize a rheostat assembly from what must have been Radio or Hi-Fi sets as they are marked with the label "volume". The leveling head screws and slow motion screw assemblies are different than current Warren-Knight units as is the battery case. The currently produced Warren-Knight 20-8403 unit is almost identical to these units with the above exceptions. This instrument type has been in production for a over 65 years with very minor changes! The instrument above is an early production unit and has rotary switches, later examples have toggle switches, and even later models a single toggle switch. The second switch is redundant to the reticule rheostat and was eliminated in later production runs.
David White of was the original manufacturer of theodolites in this series. Manufacturing facilities, were later transferred to Warren-Knight Industries. Both companies exist to this day. Warren-Knight can repair, calibrate and re-certify David White, Seiler and Warren-Knight sourced instruments. This is not an inexpensive proposition, however a new 20-8403 unit costs in the $ 8,000 range so refurbishment of an older unit will still be a substantial cost savings by comparison.
A third company Seiler of St. Louis MO. made a ML-474 specification theodolite. Very few were manufactured by Seiler (concurrently with David White production) and these instruments although operationally identical to the David White 6061 were manufactured using different tooling and methods. They look very similar but not identical.
Both David White and Warren-Knight continue production of surveying instruments to this day. David White no longer manufactures Pibal Theodolites. Other historical White Products include Stereo Cameras (Realist Series) and Mark II Sextants produced for the Navy during World War II period.