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Gurley Aero-1930-USN-No. 49-41

gurley1.JPG (51076 bytes) A side view of a Gurley Pibal Theodolite,
Model Aero-1930-USN-No. 49-41 Manufactured in 1942.  Some examples were produced with lighting for the crosshairs and verniers.  This unit was not produced with this feature, or the holes to attach the lighting related parts.
gurley.jpg (55067 bytes) The Gurley balloon theodolite has gun sites and a fixed focus objective.  The eyepiece has a focus for the cross hairs.  The telescope does not have a switchable wide angel objective. 
gurley2.jpg (49483 bytes) In this photo you can see the elevation control knob.   Note that it is not a micrometer type.  The instrument is read with a vernier scale.

On this instrument both the azimuth and elevation scales are directly above each other for quick viewing.

This balloon theodolite has a fixed focus telescope.  The eyepiece has a diopter adjustment to keep the cross hairs in focus for eyeglass users.