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PRACTICAL IMPROVEMENTS IN STEREOPLOTTING INSTRUMENTS 
by Morris M. Thompson and James G. Lewis 
U.S. Geological Survey 
In technical journals and convention programs devoted to photogrammetry, 
the greatest emphasis is usually given to new and sensational developments 
in instruments and procedures. This preponderance of interest in the 
frontiers of our science is entirely normal and healthy; but the fact remains 
that an overwhelming proportion of photogrammetric mapping is being carried 
out with classical instruments whose principles have been in use for a 
generation or more. Managers of the current-production phases of photogram- 
metry have reason to be encouraged for the future by remarkable ,? break- 
throughs" such as the development, in prototype form, of plotting machines 
whose operation is completely automatic. Nevertheless, these managers know 
that they are not going to make any maps with these instruments until the 
,r bugs" are removed or until a definite economic advantage is demonstrated. 
In the meantime, they must do the best they can with the available workhorse 
instruments that have for some years been turning out good photogrammetric 
products at a substantial rate. This paper is concerned with some of the 
things that have been done to improve production with well-established equip 
ment, particularly double-projection anaglyphic instruments. 
In the U.S. Geological Survey, the bulk of the stereoplotting work for 
topographic mapping is done with the ER-55 and Kelsh plotters. These 
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instruments are manufactured under the trade names of Balplex and Kelsh 
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Plotter, respectively. A continual series of improvements has increased 
^Prepared for the Panel on Analog Photogrammetric Instruments, Com 
mission II, International Congress for Photogrammetry, Lisbon, Portugal, 
September 1964. Publication authorized by the Director, U.S. Geological 
Survey, Washington, D.C. 
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The Balplex is manufactured by the Bausch and Lomb Co., Inc., Rochester, 
New York. 
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The Kelsh Plotter is manufactured by The Kelsh Instrument Co., 
Baltimore, Maryland.