Standard Definition and Examples in Science

Understand the Meaning of Standard in Metrology

This image depicts the International Prototype kilogram (IPK) standard, which is made from an alloy of 90% platinum and 10% iridium, machined into a cylinder. The IPK is kept at the Bureau International des Poids et Mesures in Sèvres, France.
GregL

The word "standard" has several different definitions. Even within science, there are multiple meanings.

In metrology and other sciences, such as chemistry and physics, a standard is a reference that is used to calibrate measurements. Historically, each authority defined its own standards for systems of weights and measures. This resulted in confusion. Although some of the older systems are still in use, modern standards are internationally recognized and defined under controlled conditions.

Examples of Standards

In chemistry, for example, a primary standard may be used as a reagent to compare purity and quantity in a titration or other analytical technique.

In metrology, a standard is an object or experiment that defines the unit of a physical quantity. Examples of standards include the international prototype kilogram (IPK), which is the mass standard for the International System of Units (SI), and the volt, which is the unit of electrical potential and is defined based on the output of a Josephson junction.

Standard Hierarchy

There are different levels of standards for physical measurements. The master standards or primary standards are those of the highest quality, which define their unit of measure. The next level of standards in the hierarchy is secondary standards, which are calibrated with reference to a primary standard. The third level of the hierarchy encompasses the working standards. Working standards are periodically calibrated from a secondary standard.

There are also laboratory standards, which are defined by national organizations to certify and calibrate labs and educational facilities. Because laboratory standards are used as a reference and are held to a quality standard, they are sometimes (incorrectly) referred to as secondary standards. However, that term has a specific and different meaning.