Here a a few shots of that indicator.
As you can see, not very big, but only 0.005" movement each way from zero.
It can be operated from either end, either the plunger to the right is pushed in, or the lever on the other end can be pushed sidewards into the rod sticking out, there is a little channel it runs in.

Not very thick either.
The cover plate and body has a lovely sliding dovetail fitting. Unfortunately, a little damaged at the very top left hand corner, as shown on the pic. It was like that when given to myself.

An insides shot, showing that it is actually made from a cast part, then machined up.
If you can't read the writing, it says
THE KCCH TEST INDICATOR
NYACK NY PAT. JULY 17 1906

It really is a nice unit, and if you can work within it's short working scale, perfectly useable.
Just because it is old, doesn't mean it has to be discarded.
These people have theirs identified incorrectly, as KOCH, and I also think it is a later model than mine, as it has the 1/1000th markings on it.
http://www.goantiques.com/detail,koch-test-indicator,1850590.htmlBogs