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Tamaya BT-901 Balloon Theodolite (pibal theodolite)
This theodolite was imported (from Japan) by Weather Measurement Corp in the mid 1970's it included: lens covers, spare lamps, adjusting pin and wrenches, screwdriver, dry cell case, tubular compass, bubble levels (2), light filters (3), a 4 position light filter set, and a lens shade. All items were stored in a wood case. Some models utilized a AC transformer in place of the battery case. The theodolite has a switchable wide angle finder scope, lighting for night time use, and a gun site on top of the main objective for rough aiming. This theodolite differs in design from the Gurley, and Warren Knight models in that the objective is not perfectly aligned with the horizontal center. It is offset to one side, the Watts theodolite is also off center. This limits the accuracy of these instruments if they were to be used for surveying work.
Azimuth and elevation adjustments are made with thumb wheels that worm drive gears in the theodolite (no micrometers). The gears are connected via slip clutches to the centers. The circles are connected to the centers. A complex mechanical device considering that it does not incorporate micrometers. Both circles including 10 part verniers are viewable through a window directly to the left of the eyepiece. (See the photo below) The physical location of the circles is below the eyepiece (covered by a frosted glass pain). This glass pain lets in light to illuminate the circles by day and is illuminated by two lamps for night use. The theodolite below is missing one of the rheostat knobs. The lighting for the circles and the reticule is separately controlled by two rheostats.
The ability to read the circles on the same side of the theodolite as the eye piece and and the use of a switchable mirror allowing for one eyepiece to use the two objectives are improvements over the WWII vintage theodolite by Tamaya. Two later models were produced the TD-3 and TD-4 (currently in production) are digital theodolites with RS232 outputs and optional data printers.
A The case measures 12" X 12" X 11" and the transit is 11" high and 10" wide.