It is all written down somewhere. I did some shot peening 30 years ago and there was a measurement method involving a strip of metal which you peened and then you measured how much it curled up. That gave you a number. Then you looked in the book and it told you what number to shot peen connecting rods. We shot peened factory rods after they had been deburred on a big sanding roll. That was 30+ years ago and I wouldn't waste my time with any of that crap these days. Now I just call Summit for some chrome moly BB Chevy rods and give them a credit number. The rods show up in 2 days and I bolt them in the engine.