"Mechanical Magic" wrote in message
...

Are you talking about spring calipers or sliding calipers, Dave? If we
were
to sit down and try it together I could demonstrate repeatable accuracy
in a
2" ring of +/- 0.002" with spring calipers; probably half that with good
instruments. An expert can do even better. But if you're talking about
sliding-scale calipers, they're next to useless for measuring the inside
of
a ring.

--
Ed Huntress

Ed,
I'm speaking of direct measuring sliding calipers, I have vernier,
dial and electronic.

I think they are greatly over-rated.
Dave

Yes, I agree. I have some good ones myself, including Swiss vernier types,
digital Mitutoyos, and dial Starretts. I only use them for approximate
measurements.

Spring calipers, though, are a topic unto themselves. I use them mostly for
comparative measurements but you can get surprisingly accurate absolute
measurements from them, checking them with a micrometer. They're a great
boon to the hobby machinist who learns how to use them well.

--
Ed Huntress