Quote:
Originally Posted by andrewwynn
Closer to a moiré that interferometry.if you had a long enough bolt the "beat" of interference would be evident and you could measure the stretch by the vernier.
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LOL. Sure. I have more experience with interferometry, so that's what I thought of, but I'm sure you're right. Waaay back in the day, in my first real job after trade school, I set up a laser interferometery system to calibrate some high speed CNC machines. Pretty cutting edge stuff, both literally and figuratively.
Very primitive computing back in those days, but they basically counted as the laser wavelengths passed eachother to measure the mill moving. Similar to here, where "counting" the relative movement between bolt thread patterns was 1/3 of a wavelength I knew the bolt had stretched by that much without having to actually measure anything. Just counting.