SM098     Vernier Calipers     circa 1950     Mechanics

  Vernier calipers use a special sliding scale enabling a linear measurement to be read more accurately.   A normal scale would be only readable to one millimetre, which is the normal marking on a linear scale.   But if instead of one mark on the sliding scale, there is a short scale marked such that ten subdivisions on the short scale correspond to nine on the main scale, the calipers can be read precisely to 0.1 mm.

  In reading the vernier scale, the zero mark on the short scale gives the reading to the nearest millimetre.   The number of tenths of a millimetre can be read off by noting which two calibrations on the main scale and short scale correspond most closely and adding this to the main reading.

The Vernier, which was invented by a French mathematician of that name, who died in 1637, can be applied to all kinds of linearly divided scales including degrees and minutes.   The accuracy of the readings depends on the marking of the vernier scale, which on the SM098 vernier calipers is capable of giving a reading with a precision of 0.02 mm on the centimetre scale and 0.001 inch on the inches scale.