Scans and information on the Cooke, Troughton & Simms LTD. Model S25
Balloon Theodolite.
Published specks for the Model S25 from a 1928 to 1930
catalog, Thanks to E. Ross of New Zealand..
Circles - Horizontal and vertical circles 5 inch. diameter, both
reading against an index by means of a large achromatic magnifier. The circles are
divided to single degrees and .05 degrees may be readily estimated.
Telescope - Fixed focus, bent axis type, 1.45 inch diameter 20 power i0 inch focal length. Transit axis held in screwed-down bearings.
Diaphragm (gradicule) Simple cross pattern in our interchangeable cell. 11 other styles were listed in the catalog as options.
Spirit Level - 40-45 secs to 2 mm., mounted on cover plate. (single level)
Leveling Base - Three Screw type.
Box - The instrument is packed in one piece in a mahogany box fitted with lock and key and a leather shoulder strap is provided.
Weights - Instrument only 13.0 pounds, Box and Accessories
6.0 pounds
Notes: The instrument appears to use friction wheels or tangent screws to drive the circles, but they are not specified as to having micrometer readouts. The catalog lists surveying instruments with micrometer readouts so is safe to assume that since this instrument is listed as having an index that it lacks micrometers.