Vernier caliper
The vernier caliper was developed in the 17th century. A vernier
caliper is one that has a movable scale that with another at one
time. A magnifying glass is helpful for reading the vernier lines,
but in the examples here they are highlighted.
Determining the measurement. Locate the line on the main scale that
the zero on the sliding vernier scale is lined up with, or is just
beyond. The reading on the main scale is 0.025�? If the zero lined
up exactly on the third line, then 0.075″would be the measurement.
If the vernier scale zero did not line up exactly with a line on the
main scale, runs parallel to a fixed scale. The tool will measure
outside diameter (O.D.), and inside diameter (I.D.) from 0 to 7
inches in thousandths of an inch, or from 1 to 180 millimeters. The
inside measurement is somewhat limited by the length of the jaws, so
it cannot be used deep in a hole. The vernier caliper here can also
measure depth. When the cost fo a vernier caliper is compared to the
cost of an entire set of micrometers, the reason for its popularity
becomes apparent. A vernier caliper is the most versatile measuring
tool. Every technician should one.