The relative positions of the. fiducial marks of the camera 
The determination of the shrinkage of both negative and diapositive material 
requires knowledge of the relative positions of the fiducial marks of the 
camera. This is also a condition for the use of analytical block triangulation 
in the actual experiment. For the purpose a record of the measurement results 
of the fiducial marks of the camera was obtained from Czechoslovakia. 
It is evident from the record that each of the four fiducial marks have been 
measured three times and the measurements have been repeated 10 days later. 
On examination of the measurements of the fiducial marks the fact that the ©“ * 
differences between the measurements are in several cases up to 10 microns. 
This discrepancy is larger than average. 
The position of the cross-shaped fiducial marks of the Wild instrument can be 
determined by measuring one point from each segment of line and by calculating 
the equations of the lines that pass through the two pairs of opposite points 
and by then computing the intersection point of the twp lines. If a precision 
stereocomparator is used in the measurement, the coordinates of the fiducial 
marks can be determined within an accuracy of +5 microns. In the tests that 
are described below the measurements that were taken in Finland were in the 
manner described above. 
Comparison of the distances between the fiducial marks as determined from the € © 
measurement that took place at a time interval of 10 days indicate that one 
pair of opposite fiducial marks has remained unaltered while the other pair 
has contracted ca 10 microns. Taking into account the accuracy of measurement 
this may be due to chance but it is more likely that the fiducial marks have 
been photographed onto film and an affine deformation has taken place during 
the 10 days. If the fiducdal ‘marks of the camera have been photographed onto 
glass it is difficult to perceive why the latter measurements have on the 
whole taken place. Presuming that the photographed was onto film the first 
measurement corresponds more accurately wiht the fiducial marks of the camera. 
For this reason the first set of measurements have in all following circum- 
stances been used as indicative of the relative position of the fiducial marks 
of the camera (table 1).