THE NEW «‘NISTRI, TA3|A STEREOCOMPARATOR 
The prototype of the OMI Stereocomparator Model TA3 was materialized 
during the year 1957 and was ready to work by May 1958. Even though its 
characteristics are already known by now, it will be well to sum up the principal 
characteristics of the instrument and the purposes that this instrument serve. After 
this short premise, I wish to treat briefly the following items: 
1) Modifications and improvements introduced during the manufacture of the 
instruments materialized in the last two years; 
2) Description of the new model materialized in these last months on the basis 
of a long experience acquired meanwhile. 
The fundamental characteristics of the OMI Stereocomparator TA3 are the 
following: it is fitted with three plate carriers upon which are placed three adjacent 
photographs; it is fitted with a special optical commutator that permits, at oper- 
ator’s choice, to observe one of the three following stereograms: 1-2, 2-3, 3-1. This 
allows performing the bridging in the usual manner, and furthermore always makes 
available two different models of the area common to the three photographs. 
Moreover the instrument is characterized by the complete mechanical independence 
of its three coordinatometers, both among themselves as well as from the observa- 
tion system. This feature was realized by the use of electromagnetic transmissions 
which for years have been applied to all Nistri instruments. Besides the usual mo- 
vements obtained by manipulating the hand-wheels and used for collimation, it 
is also possible to move the coordinatometers at high speed by actioning push-buttons 
placed on the control panel. 
The observation system is fitted with a luminous floating mark whose colour 
and luminous intensity can be changed at the operator’s choice. Said floating mark 
is superimposed to the photograph by means of a semi-transparent mirrors system 
inserted in the telescopic optical path of the observation unit (parallel rays). The 
observation magnification can be changed with continuity, concurrently together, 
or independently for, the two ocular systems. 
The detail under observation, with the relative floating mark superimposed, 
can be photographed together with its individualizing number, the same number 
that will automatically show in the coordinate recording of said point. 
The measure is performed by means of high accuracy lead screws fitted with 
suitable automatic correcting devices. Each one of these lead screws, actioned by 
means of syncro-motors controlled by the operator through hand-wheels, are 
connected on the opposite end to an electric contacts counter whose individual digits 
are scanned by a special selector of telephonic type. The impulses supplied by the 
selector, after having passed through the above mentioned contacts, are transformed 
into code and actuate a commercial teletype or tele-punching machine.