operator by means of a hand-wheel, which we refer to as « Z ». 
Instead of a hand-wheel « Z », a pedal-disc « P » may be used. 
The first carriage supports two cylindrical horizontal guides (paral 
lel to each other and normal to the formerly mentioned guides) 
along which is the sliding path of the «second carriage» (13.) This 
one supports two cylindrical vertical guides, being the sliding path 
for a third carriage (9). 
The second and third carriages are also made to slide along their 
own guides, actioned by screws and controlled, through a system 
of transmission, by hand-wheels which we refer to as « X » and «Y ». 
Instead of hand-wheels « X » and « Y » which must be operated 
jointly with pedal disc « P », a pantograph (of the Santoni type) 
may be used, at will. So one may employ hand-wheel « Z » instead 
of the pedal and thus achieve easier handling, better speed and 
greater accuracy both in the representation of planimetry and in 
height measurements. 
The base, on the side of the operator, supports a strong steel bridge 
carrying two guides parallel to the guides of the second carriage. 
Said bridge supports the two projection cameras whose axes, in 
the fundamental positions (cp = w = 0) are horizontal and paral 
lel to the guides of the first carriage. 
The third carriage, moving, as said before, vertically, bears two 
vertical side guides (9'-9"); along these the supports (1' 2') of 
the guide-rod (a-b) couplings may slide or rest in various positions. 
Usually, one of them has to be placed above, the other one below 
the projection centre of the cameras (distance above and below 
should be approximately the same). The difference in height bet 
ween the two joints is to represent the larger component of the 
base (Bx). Therefore, according to this peculiar arrangement, it 
turns out to be in a direction orthogonal with respect to the line joining 
projection centres (1-2). 
This allows passing (conventionally) from the «inner base» to 
the «outer base» and viceversa, by shifting vertically the two 
joints (l / and2 / ), whose interdistance is thus more or less preserved. 
This arrangement clearly yields remarkable advantages in aerial 
triangulation.