Quote:
Originally Posted by Rodger Knox
Your approach is perfectly valid, but due to the necessity of making two readings, you're not really getting any better accuracy by using the digital calipers. There's a lot of ways to do this, which usually means they all work well enough.
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Agreed.
Every measurement has some error associated with it. The more measurements one makes, generally, the larger the error associated with that measurement.
For example, there is an error in zeroing the ruler at the nut position. There is an error in placing the calliper at exactly, say, 20". There is an error associated with the calliper reading, be it small. There is an error in marking where the calliper ends. The stack-up of errors probably yields a value that is no closer to the desired value than the error of using a single ruler and eye-balling the reading to about 1/4 mm.