456 
residuals of five different circles have also been determined. See table 
2. 
Diagram I shows the variation of the root mean square value of the 
residuals with the radius. It shows an evident increase with the radius 
and the same tendency as in earlier investigations. The weight of the 
coordinates at the centre is about ten times the weight at the radius 
150 mm. 
This weight distribution might depend on irregular movements in 
the film due to tensions caused during the developing procedure and 
to a certain degree also on the resolution of the lenses. Perhaps this 
can be compensated for by increasing the precision by averaging a 
larger number of settings towards the edges according to the weight 
distribution.