CATHODE RAY 
TUBE 
Figure 3 Optical System fer B8 Sterscmat 
This allows observation, through other lenses and prisms, of the 
diapositives which are moved by the space rods relative to the 
fixed measuring mark. Appropriate filters separate the blue 
electronic light and the yellow visual light. This system thus 
provides the continual optical monitoring of the automatic 
function of the instrument.