on the face of the electronics chassis, which measures 7 inches high by 14 inches 
wide by 14 inches deep. The digitizer employs solid-state, integrated circuits 
and draws less than 50 watts of power. Productivity with the digitized model has 
been found to be about double that experienced with the standard model. 
Although the basic comparator is designed specifically to measure standard 
plates, nonstandard plates and cut film can be measured with the aid of a special 
dual focus microscope and universal stage that are offered as optional accessories. 
The dual focus microscope incorporates a beam splitting arrangement that permits 
one to focus simultaneously on the scale and on the specimen mounted on the 
universal stage. The specimen plane and the plane of the scale have a 
separation of 6 millimeters. 
We have under development for introduction in early 1969, a very compact, 
semi-automatic setting device, the scanning head of which retrofits to the dual 
focus microscope. This device is expected to provide an rms repeatibility of 
setting to better than 0.5 microns on well-defined points such as PUG points. 
CONCLUSIONS 
From the successful development of the self-calibrating, multilaterative 
comparator, an entirely new approach to the precise measurement of photo- 
graphic plates has emerged. By offering a moderately priced alternative to 
conventional comparators, the instrument has already made it possible for several 
organizations to undertake the practice of analytical aerotriangulation. We expect 
this trend to grow. 
REFERENCES 
Brown, D.C., Computational Tradeoffs in the Design of a One Micron Plate 
Comparator, presented at the 1967 Semi-Annual Convention of the American 
Society of Photogrammetry, St. Louis, October 2-5 (also to be published in 
Photogrammetric Engineering).