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ABSTRACT: A New model three plate precision atereocomparator with 
automatic coordinate recording produced by OMI-Nistri, Roma, 
Italy, is described. The principal advantages of greater 
stability, less maintenance and operator comfort are realized 
by a unique symmetrical disposition of identical measuring 
stages. The translation of the photograph measures one 
coordinate and translation of the optics measures the other 
coordinate, greatly simplifying the kinematic structure. 
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The aim of this paper is to make known the characteristics of a 
new stereocomparator and to explain briefly the concepts on which its 
structure and its attributes are based. 
The Stereocomparator Model TA3/P was conceived and designed by 
Ottico Meccanica Italiana (OMI), calling upon its vast reserve of 
technical experience in stereocomparators and analytical plotting 
instruments. 
The considerable success and the innumerable advantages of the three 
plate disposition has lead to the continued use of this arrangement. 
On the other hand, as regards the kinematic structure of the 
coordinatometers, the old type has been abandoned in favor of the design 
already successfully tested by the Analytical Plotters and which has 
given us the possibility of developing a more direct optical system 
which is less cumbersome and more reliable in its functioning. Finally 
even the analog-to-digital recording system has been completely modified 
in such way as to utilize advanced electronic techniques, which, when 
the first TA3 stereocoraparator was planned, were not yet sufficiently 
reliable. 
We shall divide the following description into three main parts: 
The mechanical structure, the optical layout, and the recording group. 
MECHANICAL STRUCTURE 
The three measuring stage groups have been positioned at the 
vertices of a quadrilateral at whose fourth vertex is placed the