Editing Operational definition (section)

== Examples ==

=== Temperature ===
The thermodynamic definition of [[temperature]], due to [[Nicolas Léonard Sadi Carnot]], refers to heat "flowing" between "infinite reservoirs". This is all highly abstract and unsuited for the day-to-day world of science and trade. In order to make the idea concrete, temperature is defined in terms of operations with the gas thermometer. However, these are sophisticated and delicate instruments, only adapted to the national standardization laboratory.

For day-to-day use, the [[International Temperature Scale of 1990]] (ITS) is used, defining temperature in terms of characteristics of the several specific sensor types required to cover the full range. One such is the [[electrical resistance]] of a [[thermistor]], with specified construction, [[calibration|calibrated]] against operationally defined fixed points.

=== Electric current ===
[[Electric current]] is defined in terms of the [[force]] between two [[infinity|infinite]] [[Parallel (geometry)|parallel]] conductors, separated by a specified distance. This definition is too abstract for practical measurement, so a device known as a [[current balance]] is used to define the [[ampere]] operationally.

=== Mechanical hardness ===
Unlike [[temperature]] and [[electric current]], there is no abstract physical concept of the [[hardness]] of a material. It is a slightly vague, subjective idea, somewhat like the idea of [[intelligence (trait)|intelligence]]. In fact, it leads to three more specific ideas:

# Scratch hardness measured on [[Mohs scale of mineral hardness|Mohs' scale]];
# Indentation hardness; and
# Rebound, or dynamic, hardness measured with a Shore [[scleroscope]].

Of these, indentation hardness itself leads to many operational definitions, the most important of which are:

# [[Brinell hardness test]] – using a 10&nbsp;mm steel ball;
# [[Vickers hardness test]] – using a pyramidal diamond indenter; and
# [[Rockwell hardness test]] – using a diamond cone indenter.

In all these, a process is defined for loading the indenter, measuring the resulting indentation, and calculating a hardness number. Each of these three sequences of measurement operations produces numbers that are consistent with our subjective idea of hardness. The harder the material to our informal perception, the greater the number it will achieve on our respective hardness scales. Furthermore, experimental results obtained using these measurement methods has shown that the hardness number can be used to predict the stress required to permanently deform steel, a characteristic that fits in well with our idea of resistance to permanent deformation. However, there is not always a simple relationship between the various hardness scales. Vickers and Rockwell hardness numbers exhibit qualitatively different behaviour when used to describe some materials and phenomena.

=== The constellation Virgo ===
{{See also|Axial precession}}
The [[Virgo (constellation)|constellation Virgo]] is a specific constellation of stars in the sky, hence the process of forming Virgo cannot be an operational definition, since it is historical and not repeatable. Nevertheless, the process whereby we locate Virgo in the sky ''is'' repeatable, so in this way, Virgo is operationally defined. In fact, Virgo can have any number of definitions (although we can never prove that we are talking about the ''same'' Virgo), and any number may be operational.

=== Academic discipline ===
New [[academic discipline]]s appear in response to [[interdisciplinarity|interdisciplinary]] activity at universities. An academic suggested that a subject matter area becomes a discipline when there are more than a dozen university departments using the same name for roughly the same subject matter.<ref>[[Rustum Roy]] (1977) "Interdisciplinary science on campus – the elusive dream", [[Chemical and Engineering News]] 55(35): 28–40</ref>