I used to Build racing 2 stroke engines and part of that involved trueing the crank.Most other other builders used to retrue so that it was within 1/1,000" and that was good enough for them. I wanted truer than that and I got it so the dial gauge just showed a shudder on the crank. Then one day a customer came in for a big end change and I put the crank back in the Lathe to check and it was perfect straight away. The customer was surprised at how I had done it so easily and I was shocked--Normally took 3 or 4 attempts to get it that perfect.