Digital Readout for measuring?

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A guy asked me once how close I get a set of  twin parts. I thought I had no way to measure it and said back then within a few thousands of each other.  I was not going to bring my big Master Bar in to do it. I don't have a tolerance and the overall length is not of as much importance as them being identical. I would just compare the parts length on a surface plate and I admit it was not the best way to do it.I did it my normal way today and when I was done it hit me. Use the darn DRO to do it dummy! Not everyone has a huge micrometer or 24" calipers but the DRO seems to be pretty common these days. I was  +.025" on my overall length (could have been .250" and nobody would have known) and .0015" of each other.I am sure it is not a new trick but it was an original idea to me.
Reply:dro need calibration checking every so often. usually use 6.0000 gage block and test indication. zero indicator and dro and remove gage block and move indicator to where gage block was resting and see what dro says..most better dro have a calibration mode where you tell it how far it went and compensates what it read. 6.0000 verses 5.9990 and adjusts the scale ratio to read more accurate. usually test each axis X, Y, Z etc. most better machine shops will check this before any critical jobs.i often measure parts with a test indicator and the dro to measure parts in spots to .0001"