The primary requirements for a comparator are stability 
and reliability of the measuring system. For convenience, 
a recording unit is attached to the comparator, which 
facilitates and significantly spreads up the measurement. 
Improper funetioning of this unit can render the comparator 
useless. 
Figure 41 shows the differences between two measurements 
of the same grid in two different comparators. There is no 
doubt that one of the eomparators performed far below standard. 
The source of the error has not yet been determined but it is 
expected to be found either in the image carrier guidance 
system or in the recording unit. A certain error pattern 
related to the mensuration sequence can be recognized: each 
line was measured from left to right, first all the points 
spaced 2 em apart, and then the remaining ones after return. 
IMAGE DEFORMATION CORRECTION 
  
In June 1970, a conference dealing specifically with 
image deformation was held at the National Researeh Couneil 
in Ottawa. The presented papers can be divided into two 
groups: those dealing with the various sources of image 
deformation ([2], [15], [201, [28], [35], [361], [40], [42], 
[14], [461], [671, [68], [74]) and those discussing the 
methods for the correction of image deformation ([ 71, [9], 
[33], [34], [36], [75]). Presented results indicated that 
a correction method which treats the entire frame as one