Compression Ring End Gap

The quick and dirty, and CHEAP, measuring tool is a digital caliper. I was a machinist, so I preferred a dial caliper, but a digital is very useful, should be in any engine assemblers box.
But I can't do without my 2-3 mic for crank journals, and 4-5 mic for pistons,(your 273 would need a 3-4, ) and a dial bore gauge for bearings and bores. I've put engines together before without them...... but I know better now.
If you don't have any of the above, head over to HF for a digital caliper today.