What do you think..

About an inch and a half long..I am sure it isn't used for any big jobs...LOL

Many of these were made for teaching and small parts. Yours has a hole in the frame to allow mounting it to a simple bench top fixture. If the anvils were lapped it would probably be just as accurate as when it was made. A view of the other side would show if it was metric or Inch, though it looks Inch to me. Has pocket wear. Nice!

I have one that is Metric and I use it quite often.

This one is smaller. Got it from my Dad, not sure what it was used for?

Keith,
That's exactly what I have in Brass. 0-10. I use it often on pinions, staffs & other small parts.

That is quite interesting... I'm measuring little stuff with my six inch analog sliding vernier rule.

It is a bear to manage this large instrument when measuring down to .004 inch on a delicate part...

It would be great to be able to put this in my super tiny clamp on bench vice and free up a hand to manage the part.

also to say you are most likely not getting the correct size with calipers anyway.. I meant to post before as Dave said probably needs to be checked, if you need faces lapped I have lapps and optical flats for doing this,