11 
ark is 
ng the 
e must 
s come 
er th e 
refore 
econdly 
noticed 
wh ich 
roup we 
rk w i th 
r this 
viously 
ane of 
system 
lower 
on the 
itching 
itself 
Amici - 
ci-Dove 
to say 
e prism 
prism, 
.th the 
of the 
.11 the 
180°, 
its own 
e, the 
e mark, 
removed 
ounted. 
greater 
arriers 
c idence 
4SP 
The last operation after the above described rectifications is 
necessarily, as in all photogrammetrie instruments, the testing of the 
precision of the whole instrument carried out with calibrated grids. 
Before beginning the test readings it is necessary to check the 
perpendicularity between the axes X and Y, to adjust the backlash of 
the screw nuts and finally to check the eventual plays in the moving 
parts. The grid plate used to check the perpendicularity between the 
axes of the co-ordinatometers is always the same and it is severely 
checked with a Genevoise laboratory equipment. 
The coordinates of the grid plate points are known with a Root Mean 
Square Error smaller than 1 micron. In order to measure the error for 
the orthogonality, readings of 9 points are made first, then, after 
having introduced the eventual correction in the way already mentioned, 
the coordinates of the 25 points of the grid plate are read. 
The residual perpendicularity error is not higher that 3" to 4". 
The elimination of the plays is made repeating several collimations 
of points suitably distributed on the grid plate, and making the 
collimation by approaching the measuring mark from opposite directions. 
This operation is particularly delicate; it is possible to eliminate 
almost completely the play of the screw-nut considering the particular 
type of screw-nut used. The residual error (checked on a test bench 
also) is most of the times in the field of 1 micron. In order to 
eliminate the plays in the kinematic system, it is necessary to operate 
on a satellite gear housed in the gear-box connecting the servomotor and 
the Quantizer to the measuring screw. 
When the adjustment is made, the total backlash must not be higher 
than 3 to 4 microns. 
As in all instruments of the Stereocomparator type, even on the 
AP/C the planimetric readings carried out on a grid, must be corrected 
by the k rotation with an appropriate calculation. It is also possible 
furthermore to introduce the correction due to errors in the length of 
the screws. On this matter, it is wise to remember that all measuring 
screws for Analytical Plotters are submitted to rigorous and severe 
testing and therefore to a sorting for the couplings on the instrument. 
In fact the electronic Computer can bring about corrections on the 
systematic errors in length of the measuring screws both for the two A' 
coordinates and for the two Y. coordinates. 
For the calibration of the lead screws used in the Analytical 
Plotters a special equipment has been built. It mainly consists in an 
AP/C Co-ordinatometer, a rule calibrated with the precision of the micron, 
and a microscope.