Least Count

The "Least Count" of any measuring equipment is the smallest quantity that can be measured accurately using that instrument.Thus Least Count indicates the degree of accuracy of measurement that can be achieved by the measuring instrument.

  Minimum measurement that can be made by a measuring device is known as " LEAST COUNT'.

  Least count (vernier callipers) = minimum measurement on main scale / total number of divisions on

All measuring instruments used in physics have a least count. A meter ruler's least count is 0.1 centimeter; an electronic scale has a least count of 0.001g, although this may vary; a vernier caliper has a least count of 0.02 millimeters, although this too may vary; and micrometer screwgauge's least count is 0.01 millimeter and of course a conventional ruler has .01m.

The Least Count is the discrimination of a vernier instrument. All measuring instruments used in the subject of physics can be used to measure various types of objects, but all do so without considering the detail of accuracy.

No measuring instrument used in physics is accurate and always has an error when readings are taken. Even the latest technology used in measuring objects also have an error where reading are concerned. Various names can be given to this error. The Least Count, uncertainty or maximum possible error are the terms normally used in a physics course, although this may vary with different syllabuses.

The error made in an instrument can be compared with another by calculating the percentage uncertainty of each of the readings obtained. The one with the least uncertainty is always taken to measure objects, as all measurements are required with accuracy in mind. The percentage uncertainty is calculated with the following formula: (Maximum Possible error/Measurement of the Object in question) *100

The smaller the measurement, the larger the percentage uncertainty. The least count of an instrument is indirectly proportional to the accuracy of the instrument.