carriage, while their distance can be varied to measure X-parallaxes. The con- 
nection of the X-Y carriage to the tracing head, mounted on another X-Y 
carriage, is by a space rod as in the case of the early Stereographometer of 
Nistri, or more recently the ITC Stereotrainer. 
X-parallax is controlled by a wheel on the tracing carriage (as on the 
B8 or the PG2). A practical profile-tracer is supplied. The optical system, en- 
larging 2x, has a field of view of about 80mm diameter. Since electron micro- 
scope stereo-photographs are always taken with convergent axes there is a scale 
difference between foreground and background. Cylindrical lenses are used to 
correct this scale difference. Luminous floating marks are applied. 
III Improvements to Existing Instruments 
a. The Planicart, model E3. 
The lower part of the instrument has been re-designed and now has four 
legs instead of three. This will, without doubt, improve stability. The question 
arises whether the Planimat will also need this modification. 
b. The Wild A10 
The K screws were re-designed to be less sensitive to temperature variations. 
The objective lens carriage was also renewed. 
It seems not unlikely that there were modifications and improvements 
on several other instruments. They have not yet been reported however.