The curves for the two cameras are shown separately in 
Pig. 38a for the radial pointing accuracy and in Pis, 326 
for the tangential pointing accuracy. The most significant 
observation made from these figures is that the pointing 
accuracy appears to be consistently better for the RC 8 
camera. Since the photographs were simultaneously taken and 
processed in the same way, this difference must be assumed 
to be due to either a different optical quality of the lens 
or differences in the used films. It ean be noticed from 
Fig. 39 that the RC 8 photography appears to have better 
contrast. On the other hand, double images ean be noted only 
in the RC 8 photographs, in the format corners at a camera 
angle of approximately 42°. 
ERRORS OF THE MEASURING INSTRUMENTS 
  
The only measuring instruments considered here are the 
comparators. They are instruments for measuring, often in 
parallel projection, image coordinates very accurately. The 
measuring means such as grids and screws must be carefully 
calibrated and, if necessary, corrected, Differences between 
a measurement of a grid in one position and a measurement of 
the same grid after a rotation of 90° indicates the amount of 
comparator error to be expected, 
Such differences are shown in Fig. 40. They are slightly 
larger than those obtained by two measurements of the same 
grid in an unchanged position (Pig. 333).