would line up with exactly one of the reference lines on the thimble if the dimension being read was 2.5176?
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Most 2-3 inch micrometers are verniered to the nearest one thousandth.............for a dimension of 2.5176, the scale on the anvil will give the reading of 2.5, and the '25' vernier will indicate a reading of about halfway between the 17 and 18 vernier lines.............on a good day, you could eye ball the total measurement as 2.5176.but........variations in hand adjustment make the final digit of 6 very iffy.............to measure to a 'ten-thou' most machinists would use other means.