Said « grid slide » is exactly like the one fitted to the shooting camera. 
If the photograph is centered through, let’s say, four of its marginal 
points of grid intersection and these points are collimated with 
corresponding points on the grid slide, and if throughout said 
process, no deformations of the photographic image are observed, 
then, of course, we may infer that also all the other intersects printed 
on the photograph will coincide with those on the grid slide. 
Whenever this is not the case, then it will be necessary, before 
plotting, to collimate successively one by one all intersects of the 
photograph and adjust them until they coincide with the ones on 
the underlying slide. This is done by actioning, through appropriate 
screws, the cams concerned which undergo adequate deformations. 
The adjusting of cams takes approximately 10 minutes. Figure (6) 
shows in outline the work performed by the correcting device for 
accidental errors of photographic images. Frame 50, the one that 
holds the photograph (ph), is fitted with two side appendices which 
help levers (52' and 52 7/ ) to support the frame itself. Said levers 
are linked by connecting rod (54). The rod carries appendix (54') 
(see also figure 7) on which rests one end of lever (55) which in turn 
is actioned by cap (56). The cap is borne by a parallelogram (57'- 
57 // -57 /// ) whose opposite end carries cam (ax). Under said condi 
tions Ax displacement of the cam in a sense normal to the plane of 
the figure (i. e. in a parallel direction to the axis of the camera) 
induces vertical shifts of the photograph. Since with this type of 
stereo-plotter the photograph is made to rotate by 90° (on its own 
plane) with respect to the conventional position, it is by said shift 
that one obtains correction of ax. 
In a like manner cam ay, with the aid of parallelogram (58', 58 ;/ ) 
cap (59), lever (60) and lever (53) performs the correction of ay 
inside photograph-holding frame (50). Caps (56) and (59) afford 
free rotations of disc (24), when setting K value. 
Since the shift ratio of Ax and Ay cams to the ax and ay of the 
photograph is 40 : 1, if we want a correction to 0,005 mm. accuracy 
on the photograph, then we must set for each cam respectively 
a 0,2 mm. deformation. In view of reducing the size of correction 
cams, the device was so built that the cam reproduces only at 1 : 3 
scale the surface of the photograph (23 X 23 cm.).