- 47 - 
their radial distance from the center and radial and tangential 
residuals were computed in recognition of the faet that image 
quality is & radial function. The group mean Square values for 
padial and tangential pointing accuracy were then used to 
derive second-order curves shown in Fig.s 37 and 38. The 
funetions expressing the correlation between radial pointing 
accuracies and the radial distance are in Fig. 37a given for 
235 targets photographed with a Wild RC8 Reseau camera, 
2290 targets photographed with a Zeiss RMK AR 15/23 camera, 
308 eollimator images photographed with both cameras, 
575 circular targets, 
2089 negative reseau Crosses, and 
2312 positive. resesu crosses. 
The tangential pointing accuracy funetions are given in 
Fig. 37b. In order to reduce the number of curves, one 
curve only is given for the targeted points and one for the 
collimator images. The curves indicate the following correla- 
tions between the measuring accuracies and the radial distance: 
circular targets - no correlation 
positive reseau crosses — no correlation in tangential 
direction, slight correlation in radial direction 
negative reseau crosses - slight correlation in both 
directions 
collimator images - stronger correlation, particularly 
for radial distances larger than 11 cm 
targets - stronger correlation than for the collimator 
images.