this is my favorite tool:
The coaxial indicator is a great tool for indicating in or around a hole. It also works as a general purpose edge indicator. I had a very critical work piece to indicate in today. Using this I can center indicate in under 30 seconds. Using a typical dial indicator usually takes longer and requires a mirror so you can see the dial when it is facing away from you. I’ve seen students take up to 30 minutes to get it right.
Anyway, I indicated in this critical work piece to my satisfatction, then asked my workmate to double check my center using his dial traditional indicator. we were within 3 ten-thousandths (0.0003) of each other on something that has a tolerance at least 15 times larger than that. I’ll call that a win. If you don’t know how to use one, ask me sometime and I’ll be happy to show you. cheers!