Calibration: What Is It?

When members of just about any profession talk among themselves, they usually use specialized terms they all understand-jargon. There is usually consensus among them about the meaning of the terms, but they often forget newcomers or interested parties from other fields may not have the same understanding. There are also cases in which the common use of a word is different from or even opposite its technical definition. "Metrology" and "calibration" are two such words.1

The International Vocabulary of General and Basic Terms in Metrology (VIM) is an internationally accepted document that provides technical definitions of metrology, calibration and many other measurement related terms.2

Why do we need to refer to this technical glossary instead of a common desktop dictionary? One reason is the VlM is a listed authoritative reference in ISO 9000 and ISO 10012. Another reason is technical dictionaries and glossaries define the accepted technical meanings of terms, while common dictionaries merely record the ways words are used or misused in a language and most of their meanings.

According to the VIM, metrology is "the science and practice of measurement."1 Metrology is important in some way to every human endeavor. More specifically, it is critical to all the physical, chemical and biological sciences and the technologies and manufacturing processes that flow from them.

In daily life, metrology affects us in commerce and law enforcement and in regulated industries such as healthcare and aviation. Whenever you purchase a gallon of gasoline or a pound of onions, drive by an officer with a radar gun on the highway or have an electrocardiograph taken, you have directly interacted with metrology by means of a calibrated measuring instrument. One practical application of metrology-a subset of the whole field-is the system of ensuring measurements conform to certain defined relationships.

A Process of Comparison

Broadly speaking, calibration is the process of determining the relationship between the readings obtained by a measuring instrument or system and the applicable units of some defined system of measurement. According to records uncovered by archaeologists, people have been doing this for at least 5,000 years. At first, units of measure were often based on things such as the volume of grain that could be held in two hands (cup) or the distance between the...