Types of Measuring Standards (metrology)

There are 3 types of measuring Standards


  1. Line Standard
    • Imperial Standard Yard
    • International Standard Prototype meter
  2. End Standard
  3. Wavelength Standard


1.Line Standard:

According to Line standard, the distance between Inscribed lines on a bar of metal are considered as standard length under certain conditions of temperature and support. 

Line standard is of two types:
  • The Imperial Standard Yards
  • International standard Prototype meter


a)The Imperial Standard Yards

  • This standard served its purpose from 1855-1960.
  • It is made of 1 inch square cross section bronze bar and 38 inches long.
  • The bar has a  1/2 inch diameter and 1/2 inch depth, which are fitted with a 1/10th inch gold plug.
  • The gold plug contains three transverse  and two longitudinal engraved lines lying on the neutral axis of the bronze bar.
  • The yard is defined as the distance between two central transverse line on the plugs when the temperature of the bar is constant at 62oF, and the bar is supported on the rollers in a specified manner to prevent flexure (bending).
  • Secondary standards are also made as the copy of the above international yard.
  • To prevent the gold plug from accidental damage, it is kept at the neutral axis.
  • The neutral axis remains unaffected even the bar bends.

b)International Standard Prototype method




  • The prototype was made in 1889, its length made equal to the previous French standard "Meter of the Archives".
  • International Prototype  Meter bar, made of 90% platinum - 10% iridium alloy.
  • The bar was given an X  cross-sectional shape to increase its stiffness-to-weight ratio.
  • The graduations are on the upper surface, which coincides with the neutral axis of the section.
  • The top surface of the meter is highly polished and has two fine lines marked over it.  
  • The length of the meter is defined as “the straight line distance, at 0°C between the center portions of pure platinum-iridium alloy.
  • Total length of the meter is 102cm
  • This was the standard of length for the SI (Metric system) from 1889 until 1960.
  • The length of the meter was defined by the distance between two fine lines graduated on the central rib of the bar near the ends, at the temperature of freezing water (ie., 0°C).




2. End Standard


When the length being measured is expressed as the distance between two surfaces or ends, this is known as end standard.
They are time consuming to use and prove only one dimension at a time.
End standards are highly accurate and well- suitable to close tolerance measurement.
Close dimensional tolerance as small as 0.0005 mm can be obtained.
They are subjected to wear on their measuring faces. Also wringing of slip gauges leads to damage.