The micrometer below shows by the scale on the
barrel that the measurement is more than 17 mm but less than 17.5 mm. The
horizontal line running down the barrel points about halfway between the 0.20
mm mark and the 0.21 mm mark on the thimble. Therefore, the reading of the
caliper is 17.205 mm. The last digit came from estimating that it was half way(0.5) between the 0.20 mm mark and the 0.21
mm mark on the thimble.
In conclusion, a meter stick and
the vernier caliper both measure to a tenth of a millimeter with the vernier
being more precise whereas the micrometer measures to a thousandth of a mm
which is a millionth of a meter and thus the term micrometer!