3 
which aim at joining together film strips. The film plate carriers in 
fact have been conceived especially to hold two photographs each of 
9" x 9" with the additional advantage of being able to examine more than 
half of each photograph, thus allowing in every case the location and 
measurement of the principal point. 
A method of measuring and of transversal tying of strips has been 
devised by Prof. Cunietti of the Centro di Addestramento e Studi 
Fotogrammetrici of Polytechnical School of Milan. 
In addition to the above-mentioned advantages of the placing and 
the mechanical structure used in this instrument, there is yet another 
feature to be considered - and this is an advantage of great importance - 
the possibility of having easy and rapid access to the guides, upon 
which the intrinsic accuracy of the instrument depends, in order to 
align and calibrate them appropriately or to substitute them when needed. 
This technique has already been sufficiently experimented with on 
our Analytical Plotters with definitely favorable results. 
All adjustments and calibration devices of the instrument are 
within easy reach and present no difficulty whatsoever once the dust 
hood has been removed. 
Still another feature of the coordinatoseters is the complete 
protection provided the screws from dust and other foreign bodies. A 
special sheath has been developed which covers the screw completely and 
which can be removed for cleaning, lubrication and calibration when 
necessary. 
OPTICAL SYSTEM 
Each of the three coordinatometers, oriented as mentioned above, 
includes an optical group which images the photograph on the floating 
mark and also a projection lens which constitutes the first element of 
a telescopic system whose second element is shared and is located in 
the observation group. 
In the path of parallel rays between the projection lens and the 
second telescopic element are located all the prisms to which image 
rotation and selection are entrusted. 
At the beginning of the path of parallel rays emerging from the 
projection lens are the Dove prisms whose job is to correctly orient 
the image in relation to the operator's eye, thus compensating for the 
rotation due to inclination of the observation axes with respect to the 
plane of the photographs. It also allows for rotating the image in order 
to compensate for tilted photographs. In addition it permits rotating