Society of Photogrammetry, the writer drafted a proposed standard test for 
stereoscopic plotting instruments early this year (See Appendix). This proposed 
standard test has been discussed in several informal meetings of interested indivi- 
duals in the United States and was presented for discussion at the Joint meeting 
of the European members of Commissions II and III, held in Brussels, 28 through 
31 March 1951. 
In preparing this test an effort was made to meet the requirements for sim- 
plicity and still provide a test which is adequate for meeting the stated purpose of 
providing a means applicable to all types of plotting instruments for indicating 
the state of adjustment and accuracy of the instrument. In the proposed test as 
drafted, the measurements to be made have been reduced to what is believed to 
be a minimum. There are, of course, many other types of measurements and tests 
which can be made and a number of additions to this test have been suggested by 
those who have reviewed it. 
All of these suggestions have merit and should be given careful consideration 
in formulating an acceptable standard test. However, the whole purpose and 
intent of the standard test will be defeated, if too many special purpose tests are 
included, since these will complicate the problem of making the test applicable to 
all types of instruments and result in a mass of data which will be difficult to 
analyze and understand. The major suggested modifications or additions are as 
follows: 
(1) That the standard grid dimensions be altered so that measurements will not 
be made so near the extreme corner of the net model as would be required 
by the test as outlined. 
(2) That additional grid lines be added to the standard grid to provide more 
points for measurement. A five or ten millimetre grid spacing has been sug- 
gested. 
(3) That te grid be designed to simulate terrain with high relief to give a closer 
approximation to production conditions. 
(4) That the test include a method for checking and specifying the resolution of 
the optical system of the plotting instrument. 
(5) That the test include a simulated control bridge with grids through a num- 
ber of overlaps to indicate any errors of adjustment which introduce system- 
atic errors in bridging. 
Comments on this proposal to develop a standard test for stereoscopic plott- 
ing instruments and on the specific details of the test are invited. 
APPENDIX 
PROPOSED STANDARD TEST OF STEREOSCOPIC 
PLOTTING INSTRUMENTS. 
I. Purpose. — The purpose of this test is to provide a uniform basis for 
checking and specifying the accuracy and precision of stereoscopic plotting instru- 
ments of all types. 
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