The virtue of the older MicroVu is its suited for the open shop. It's crude, simple, light, and bullet proof. I keep mine near the grinder to check out threading tool angles, Acme tool tip widths etc. I use the #16 screen which has cross lines and a protractor circle. 10 and 20 x is about as strong as you ned for work like this. I use travel indicators exclusively for linear measurement and the protractor and cross lines for angles. Radii I check by rectangular coordinates if accuracy is paramount otherwise I match up a draftman's plastic circle template and work the math. I have a set of stage centers but I seldom use them. I recently converted it to LED illumination. It makes brighter images on the screen you can see in ambient light.
A further advantage to the MicroVu is it's light and rugged. You can move it around the shop where you need it. Mine works in projection mode and reflection. I have yet to use projection for anything serious but it works great for finding little slivers.
If you calibrate it as suggested above and make printer overlays on transparent film you can almost cuplicate the accuracy and convenience for inspecting small part configurations found in higher end non-electronic models.
Higher end optical comparators belong in the inspection room where their many features can be better exploited.
If you're looking for a 10" or 12" comparator for open shop use look closely at an older lower end MicroVu.
If you require one-placement whole part silhouette inspection hold out for a better class of comparator. MicroVu's optics and stage motions are not up to 0.0001" resolution.
Theres an outfit in Las Vegas that sells ands services optical comparators:
http://www.gaging.com/st.htm
There's no point is even contacting MicroVu for assistance with their older models. They will not help you. Period.
These people have screens:
Optical Comparator - J&L Metrology Optical Comparator, Sales, Service, Parts, New and Recertified Optical Comparators. There's many like this you can Google under "optical comparator screens" If you have a glass screen and wish different graduations on it you can send it in for reprinting and save a hundred bucks.