1. Plate Previewer 
The first table constitutes the plate previewer. It provides the 
means by which an operator can align the fiducial markings of a photo- 
graphic plate with the x and y axes of the measuring table, and then deter- 
mine the rough coordinates of all images of interest on the plate. It con- 
sists of: 
a) A supporting base structure. 
b) xand y axis carriage ways, with fast and slow speed elec- 
tric drives, and a magnetic clamp automatically operated when the drive 
signals are removed. 
c) A revolving plate support mounted on the cross-slide, to 
allow for 3609 rotation of the plate, with capability of vernier alignment 
to 0. 19. 
d) A light source for illumination of the plate, and a low power 
viewing system with remote eyepiece and headrest. 
e) A metering device along each axis to continuously monitor 
table translations with an accuracy of +10 microns. The zero reference 
can be selected at any point along each axis. 
f) A visual readout at the top of the previewer which continu- 
ously displays the position of the table along each axis with respect to the 
selected reference point. 
g) A control panel which permits the operator to enter certain 
commands to alter the subsequent routine of the Automatic High Accuracy 
Comparator. 
Associated with the previewing operation, and located in the op- 
erator's area, are an IBM Type 026 card punch, and a paper printer. 
These furnish the digital recording from the previewer system. 
A ten-decade keyboard, shared by the previewer and the high 
accuracy comparator, provides a means of entering numerical constants 
into the output records. 
2. Automatic High Accuracy Comparator (AHAC) 
The second measuring table in the operator's area is associated 
with the high accuracy comparator. It provides a means by which an op- 
erator can align the fiducial markings of the photographic plate with the x 
and y axes of the table, and make an initial setting of the plate position