On a Vernier scale, the width of an object is measured by reading the units and tenths part of a measurement from the lower scale (under the black region that is to the left of the cyan zero). The hundredths part of the measurement comes from the upper scale, where the red and cyan lines align. The distance between marks on the upper scale is 0.9 of the distance between marks on the lower scale.
[1] J. Bryant and C. Sangwin, How Round Is Your Circle?: Where Engineering and Mathematics Meet, Princeton, NJ: Princeton University Press, 2008, pp. 81–82.
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