5 
Figure 3.--Basic universal frame as used with ER-55 projectors. 
To assure the maintenance of surface flatness within the tolerances stated 
above, a checking procedure has been developed, utilizing the Planekator equip 
ment shown in figure 4. This equipment consists of a precise surface plate 
with a gauge for measuring uniformity of clearance between the surface plate 
and the granite table top. 
The new electrical system, designed to function with the universal table 
frame, is a decided improvement over past systems. It permits either 8-volt 
or 20-volt operation and affords convenient control over all other electrical 
devices, including the various light-balancing systems. The control panel for 
the electrical system is mounted at the right end of the table (see figure 3).