jim rozen writes:

I have recently also found a very curious micrometer, with
mechanical counter display. It has a metric display and
metric screw, but the display is in the form of two lines
of digits in a window. The rightmost digit is simply
printed on the thimble, but the left digits are printed
on pentagonal prisms that are designed to rotate once
for each turn. Each prism has even or odd numbers printed
on it, 1 thru 9 or 0 thru 8. As the thimble turns,
each turn causes the prism to present the next face
to the user.

So they can provide all the needed digits for a 1"
metric micrometer, in one window with only two numbers.

I can't visualize this. Can you find a picture of it somewhere?

Dave