I recently got these calipers and love them! Before, I only had the simple little brass ones - which are no good for measuring anything specific, only if you want a 'close' measurement.
A friend of mine had gotten some recently and mentioned how much she loved them. I decided to get a somewhat mid-ranged version. Though I found the selection rather strange. Several were in the $27 - $34 range. The one I got was $45 and then the expensive ones were $169. Quite a big jump! I can't say I really had a lot to go on when trying to decide between the different ones. But I am very happy with the one I did get. I really don't know how I lived with it!
It measures both outer diameter
and inner diameter
and you can convert the measurement from mm, to inches in either a decimal or fraction.
So far in the short time I've had it, I've used it to measure settings, stones, drill bits and burs. Maybe b/c I'm not THE most organized, finding the right size bur is just a guessing game most of the time. Now I can whip these out of their handy case and know the exact size! And yes, the come in their own nice blue case, a battery to get you started and an extra battery! You don't actually have to turn it on, just open them and it automatically turns on. It might have an automatic shut off, though I haven't tried leaving them on long enough to find out. (I'm sure they came with instructions, I rarely bother reading them unless I need to!)
If you do any stone setting, these are a big time saver. Even if you don't do much stone setting, I'm sure once you have these, you will find things to measure just for fun! I ordered mine from Rio Grande. Though I'm pretty sure Lowe's and hardware type stores carry some as well.