(518) 
substituting, we have 
(dh) (dp) f or «dpydf 
du hu (dp hu (b 
(Equation III) 
tan angle dip — 
This is the equation to use for the calculation of dip. 
B. Procedure Step by Step. 
1. General. 
Two cases are presented here; the first is the measurement of the inclina. 
tion of a dip slope, and second, the dip of strata exposed as bedding traces. 
Both cases are significant to geologists, but generally only the first of signifi- 
cance to other workers. 
2. Measurement of the Inclination of a Dip Slope. 
The pocket stereoscope should be used in steps b, c, and d. 
a. Locate carefully and mark the photo center of each photograph of the 
stereo pair at the intersection of lines joining opposite fiducial marks (fig. 3). 
b. Carefully locate and mark with a needle point the point on each photo- 
graph of the stereo pair corresponding to the center point of the other photo- 
graph. This point is called the transferred center (tci or tc;). 
c. Using the stereoscope, locate and mark on the right-hand photograph 
two well-defined points, as far apart as possible on a slope, one directly down 
dip from the other. 
d. Transfer and mark with a needle point these two points to the left- 
hand photograph. 
e. Place on the right-hand photograph a transparent sheet of acetate ap- 
proximately the same size as the photograph on which a straight line is ruled 
across the center on the underneath smooth side. Orient this transparency so that 
the line passes through both the photo center and transferred center. 
f. Mark with a sharp-pointed pencil on this transparency overlay the 
three points corresponding to the photo center and upper and lower points. 
g. Place the transparent overlay on the left-hand photograph, oriented so 
that the ruled line on the transparency passes through both the center point 
and the transferred center, and so that the upper point marked on the trans- 
parency coincides with the upper point on the left-hand photograph. 
h. Mark on the transparency with a sharp pencil point, the points cor- 
responding to the photo center and the lower point of the left-hand photo- 
graph. The distance from the photo center to that of the previous center as 
marked on the transparency is bu. 
i. Shift the transparency so that the lower point marked on the trans- 
parency from the right-hand photograph directly overlies the corresponding 
point on the left-hand photograph, and so that the ruled line still passes 
through the photo center and transferred center. 
j Mark on the transparency the points corresponding to the photo 
center and the upper point of the left-hand photograph. The distance from the 
photo center to that of the right-hand photo center marked on the trans- 
parency is bu. 
k. The distance on the transparency between either the two points 
marked for the upper point, or between the two points marked for the lower 
  
| Left ha 
The 
showing 
between 
The 
u, 
cjl, and