Ronnie has it right - I use one all the time. It is also a great idea to pickup a ring end gap filer - has a little diamond wheel and a crank on the side. Is MUCH easier than using a hand file. (But they do remove material FAST - especially on cast-iron only rings).
I always buy "file to fit" rings - so that I can set my end-gaps to be exactly what I need.
, now just chasing a .10 Amp drain on the battery ?.
Kpar
Lawrie, take a look at OEM Tools 25083.
It's nice to know there are still a few that actually measure ring gap. Most shops that I am aware of, simply remove the rings from the package, install and "done".