unitthat

Unitthat is a coined term used in theoretical discussions of measurement to denote a hypothetical meta-unit that measures properties of unit systems rather than physical quantities. It is not an official unit and has no standard definition in metrology. In its typical usage, a unitthat functions as a placeholder for the complexity or cost of converting quantities between different unit systems. It is intended as a pedagogical tool to discuss issues of dimensional consistency, normalization, and the practicality of preferred base units.

In practice, a unitthat is defined within a given thought experiment or classroom exercise and may be assigned a numerical value to reflect factors such as the number of conversion steps, the extent of rounding, or the cognitive effort required to perform a conversion. Because it is not standardized, the value and interpretation of a unitthat can vary between authors, contexts, and unit systems. The concept is primarily educational and exploratory, used to illustrate how unit choice affects simplicity, error-proneness, and interoperability across domains such as length, time, and mass.

The term has appeared in online discussions and some instructional materials since the early 21st century, but it has not been adopted by official bodies such as the BIPM or SI. As such, unitthat remains a speculative construct rather than a recognized unit in science or engineering. See also: dimensional analysis, base units, unit systems.