My triple beam scale is accurate to +/- 1/10 gram. I weigh the entire reciprocating assembly- - - -piston, wrist pin, and rings, find the lightest one, and file, grind, or machine each of the other pistons to make them all match. A dollar bill weighs almost exactly one gram. I also have a ball bearing holding fixture to weight-match the ends of the connecting rods to the same tolerance, including the rod bearings, for big end weight matching. That's standard procedure on race engines.
Jerry
