The possible effects of the weight of the linkage on the base carriage are compensated 
for by means of suitable counterweights. 
All guide rails are cylindrically precision-ground, with the same care as theodolite 
axles. 
The floating marks, which were mounted at a distance of 450 to 750 mm from the 
image plane in the A5, depending on the focal length and linkage position, are now 
mounted at a fixed distance of only 70 mm below the image plane in the vertical tele- 
scope of the prism carriage, and rigidly connected with the points of suspension of the 
linkage rods. The optical path of light between picture and floating mark is thus limited 
to a minimum and comprises no movable optical or mechanical elements. 
A5 A7 
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All these modifications guarantee an increase in precision. 
The new arrangement of the floating marks also simplifies the adjustment of the 
machine. This adjustment simply consists of leveling the base plate, the base carriage, 
and picture frame, including the linkage articulation by means of a bubble level. After 
the rods have been set in their vertical position by means of the z-drive, the floating 
mark and center mark of the frame are aligned with the axis of the linkage by means 
of two small adjustment screws. This extremely simple fine adjustment is carried out 
from operator's seat with hardly any loss of time. 
Great care has been given to the adaptation of the viewing system for efficient oper- 
ation. Optical exchange of the pictures before the left and right eyes, a switch for the 
correct viewing of slides, individual or joint picture rotation of about 1008 for con- 
version of vertical into horizontal parallaxes, all go toward making the machine as 
practical as possible. The high resolving power of the coated viewing optical com- 
ponents with any desired magnification from 6 to 10X through the exchange of eye- 
pieces meets all requirements.