The caliber, micrometer, caliper, callipers, or Vernier, is an instrument used to measure dimensions of small objects, from centimeters to fractions of millimeters (1/10 of a millimeter, 1 / 20th of a millimeter, 1/50 of a millimeter). On the scale of inches has divisions equivalent to 1/16 of an inch, and, in its vernier scale, 1/128 of an inch. It is used by designers and architects to greeks and romans since at least the sixth century B.C.
It is an instrument delicate and must be handled with skill, with care not to scratch it or bend it (in particular, the colisa of depth). It consists of a "rule" with a square at one end, on which slides another intended to indicate the extent on a scale. Allows to estimate lengths of 1/10, 1/20 and 1/50 of a millimeter using vernier calliper. By using special parts in the upper part and in its end, allows the measurement of internal dimensions, and depths. It has two scales: the lower one millimeter and the top in inches. the current gauges digital give greater accuracy and ease of use.