10 
agree within 10 meters, the self-check is satisfactory and the calculator 
signals the operator to continue. If the difference is more than 10 meters, 
the program automatically goes back to the previous step and the operator 
repeats the index point measurements. If the difference is still excessive, 
the equipment is probably malfunctioning. 
h. Assuming normal operation, the operator can now determine the posi 
tion and elevation of any point in the area of overlap between the two photos. 
To determine the coordinates of the point previously identified from stimulus 
materials, the operator enters the assigned identification number for the 
point in the keyboard, views both photos through the Stereotope, and centers 
over the point while adjusting the X-parallax and Y-parallax controls. The 
operator then signals the calculator and, within 10 seconds, the UTM coordinates 
and elevation in meters are printed out automatically together with the point 
identification number and UTM zone number. If the point lies within 50 km 
of the edge of a UTM zone, the coordinates for both UTM zones are printed out. 
These data may be stored on the tape cassette or may be transmitted via tele 
typewriter to the user. The whole operational procedure can be completed in 
less than 5 minutes. 
System Performance - Results from tests conducted with the APPS illustrate 
the type of performance to be expected. In one test, points of interest 
were identified on reconnaissance photographs with a scale of approximately 
1:5,000. These points were then identified on the data base and measured 
with the APPS. The locations determined with the APPS were compared to