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Watts  Pilot Balloon Theodolite (Mark A).

This page features an image of a catalog page from "Watts Surveying and Engineering Instruments"  Version R134.  No date is available.  I estimate it to be around 1927.

The Pilot Balloon Theodolite here is most likely what we would refer to as a Mark A or Mark B.  Since it is not listed as a Mark B, it would be reasonable to assume that it the former.   The Diaphragm "D" is a simple crosshair design.  So it does not support the tail method.  However ruled diaphragms were available.  

image of a page from an early 20th century E. R. Watts Catalog

Special Thanks to Herb Gold for Supplying the Watts Catalog Information.