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A calliper (American spelling: caliper) is a measuring instrument used to measure the distance between two opposing sides of an object between two 'legs'. An example of a dial calliper is show in figure 1.

Fig 1: Labelled diagram of Callipers


In figure 1:

  1. The outside jaws, used to measure the width of an object.
  2. The inner jaws, used to measure the separation between two points or often the internal diameter of an object
  3. The fine 0.1mm dial showing the current separation between the more coarse 10mm increment scale (4)
  4. Coarse 10mm scale
  5. Adjustment wheel, which adjusts the opening of the callipers
  6. The depth probe, not callipers at all which is used to measure the depth of a container or hole

The technique used to obtain the measurement varies but the forms you are likely to encounter in a physics laboratory:


  • Dial callipers, as shown in figure 1, which reads the final fraction of a millimeter on a simple dial.
  • Vernier callipers, which use a Vernier scale to give a direct reading with a high degree of accuracy.
  • Digital callipers which replace the dial on dial callipers with an electronic display which outputs the reading directly.