The two line drawings are mounted on a rigid backing and ‘joined together 
by a sliding arm In such a way that they can be moved In the x-direction. The 
Image separation distance may be read to the nearest 0.! Inch from the scale mounted 
on the sliding arm. 
THE SLOPE CONVERSION CHART 
The Slope Conversion Chart (fig. 3) incorporates the relationship of exag- 
gerated angle of slope, true angle of slope, and exaggeration factor Into a graph. 
By use of this graph, with any two of the three above-mentioned quantities given, 
the third can be rapidly determined. 
OPERATIONAL PROCEDURE 
By using the Stereo-slope Comparator exaggerated angles of slope can 
be determined. However, In order to convert these angles of exaggerated slope to 
angles of true slope, it is necessary to compute an exaggeration factor from a con- 
structed stereoscopic model such as the Supplementary Slope Model. In the 
following paragraphs the step-by-step procedure of computing true angles of slope, 
using the Stereo-slope Comparator, the Supplementary Slope Model, and the Slope 
Conversion Chart, is explained. 
|. Determine the true slope represented by the Supplementary Slope Model 
for the focal length and average photo base of the stereoscopic pair that you are 
using. The angle of slope represented by the Supplementary Slope Model may be 
determined from the table on the right hand side of the model. (Example: if the 
focal length of the taking camera is 81 inches and the photo base is 3.3 inches, then 
in relation to the selected photography, the Supplementary Slope Model would repre- 
sent an angle of 21°. If the focal length of the taking camera Is 6 Inches and the 
photo base is 3.8 inches then the Supplementary Slope Model would represent an 
angle of 14°.) 
2. Measure the exaggerated angle of slope of the Supplementary Slope Model 
by means of the Stereo-slope Comparator. The Supplementary Slope Model should be 
alined under the stereoscope so that a line connecting the centers of the Supplementary 
Slope Model is vertically below and in alinement with the centers of the eye pieces 
of the stereoscope. Shift the right and left members of the slope model in the x- 
direction until good stereoscopic vision is obtained. Read the amount of this separa- 
Hon from the sliding arm of the slope model. This is the image-separation distance 
and this same separation must be maintained when viewing the vertical aerial photo- 
graphs under the stereoscope.