INTRODUCTION 
In many flelds of photolnterpretation, such as geologic and engineering 
studies, an accurate determination of angles of slope is essential. These angles 
of slope are generally exaggerated in the stereoscopic model of two vertical 
aerial photographs. The true angle of slope can be determined by photogrammetric 
measurements, or in contrast to this an interpreter can estimate the exaggerated 
angle of slope and by various methods convert it to a true angle of slope. The 
first method is accurate but time consuming, whereas the second is fast but not 
always reliable. The method described In this paper takes a middle course between 
these two methods. It approaches the accuracy of photogrammetric measurements 
but at the same time considerably reduces the time needed for such determinations. 
By use of the Stereo-slope Comparator (also known familiarly as the Super-Duper 
Dipper) the exaggerated angle of slope Is measured in the stereoscopic model. This 
angle of slope Is then converted to a true angle of slope by use of two other devices, 
the Supplementary Slope Model and the Slope Conversion Chart. 
The Stereo-slope Comparator was designed for use under a stereoscope 
that accommodates an Image separation of 6.5 to 10.5 inches. The stereoscope 
should be of the straddle type or one mounted on a projecting arm which is bolted 
to the desk or work board, The field beneath the stereoscope should be unobstructed 
by the supporting stand. 
In using this method, the only required information is the focal length of 
the camera used in taking the pictures and the average photo base of the two pictures 
constituting the stereoscopic pair.