4. Measure an exaggerated slope in the stereoscopic model from the 
aerial photographs with the Stereo-slope Comparator. The aerial photographs must 
be alined under the stereoscope in a manner similar to that used for the Supplemen- 
tary Slope Model. It is essential that a line connecting the centers of the stereo- 
scopic pair of photographs be vertically below and in alinement with the centers of 
the eye pieces of the stereoscope. Care must be taken to maintain the same image 
separation that was used when measuring on the Supplementary Slope Model. The 
  
v i" 
Stereo-slope Comparator is then placed on the photographs with one target over each 
image (fig. 6). The separation, the horizontal swing, and the slope angle motions 
» Né, 
Figure 6. -- The Stereo-slope Comparator oriented + 
over the aerial photographs 3 
+ y 
are adjusted until the inclination of the targets 
Is in visual agreement with a selected angle of 
model from the photographs. The number of degrees of the exaggerated angle of 
slope is then read on the Instrument dial. Several readings should be made to assure 
consistency in setting the targets at the proper inclination. 
+ seen stereoscopically as one target, 
exaggerated slope in the stereoscopic 
5. Determine the true angle of slope from the Slope Conversion Chart, 
using the exaggeration factor determined in step 3 and the exaggerated angle of slope 
obtained in step 4. (Example: |f the established exaggeration factor for the stereo- 
scopic pair of photographs is 3.9 and the measurement of the exaggerated angle of 
: "ni te 40° x * 
slope on the stereoscopic model from the same pair of photographs is 40°, then from 
the Slope Conversion Chart, the true angle of slope would be 129.)