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 0.025â€? If the zero lined up exactly on the third line, then 0.075â€³would 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.