'ent dark area, 
foot black disc 
e the positions 
posure. 
ich 1s attached 
ated about the 
10rizontal one. 
ted a series of 
ies the shadow 
| recent flight 
1 overcast, the 
6, indicating a 
It is illustrated 
ring is divided 
segments vary 
a pole casts a 
g the white in 
10 shadow” to 
  
Fig. 8 
attenuation approximately minus 10 db. 
clockwise order: 0.89, 0.63, 0.40, 0.25, 0.16, 0.10, 0.063, 0.045.) 
Strong shadow > 
g , (Segment reflections in 
  
  
ally used for 
  
uperfluous.) = 
I Fig. 9 
(4 X 4 X 8 ft. Weak shadow, attenuation minus 3 to 4 db. 
nd to provide 
Ihe ratio of lines per mm between steps is/2. The actual value of lines per mm 
tS Evo ot the on the film for each step will, of course, depend on the scale of the photography, readily 
rightness ratio determined by measuring the length of the image of the whole platform. 
The targets 
nd vice versa. are shown in Figs. 5 and 6. 
15