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and interferometric metering devices preparatory to the fully automatic 
measuring process. It then provides for the automatic high precision 
measurement and readout of coordinates of all images dealt with in the 
output data record received from the plate previewer. 
The Automatic High Accuracy Comparator consists of: 
a) A supporting base structure. 
b) Acoordinate table with rotary platform mounted on x and 
y axis Ways. 
c) Servo controlled x and y axis drive systems controllable by 
the rough coordinates data cards prepared in the previewer, or by manual 
or image sensing means. 
d) A servo-controlled, variable-power optical system which 
permits visual observation of images, and which can sense the centroid of 
area of images within its field of view and transmit control signals to drive 
the centroid to the center of the field. 
e) A coordinate metering system along each axis to continuous- 
ly monitor table translations. The metering system will have a least count 
and absolute cumulative accuracy of 0.25 micron. The zero reference a- 
long each axis will be capable of being set at any point along the axis. This 
can be done independently of the zero reference selected in the previewer. 
f) A visual readout at the top of the high accuracy comparator 
which will display the position of the table along each axis with respect to 
the selected reference point. 
g) A control panel which permits the operator to control table 
motion during initial alignment, to select a desired magnification for the 
visual optical system, and to assume manual control over the me asuring 
process when desired. 
Associated with the high accuracy comparator operation, and lo- 
cated in the operator's area, are two IBM type 026 card punches, one of 
which is used as a reading device, and a paper printer. One punch and 
the paper printer furnish the output record of the comparator system. 
The keyboard mentioned in the description of the previewer 
position is also available for use by the high accuracy comparator opera- 
tor in inserting new constants into the output record card and printed paper.