Quantity value, numerical value and unit
A numerical value depends on the chosen unit.
Key knowledge
A quantity value combines a number and a reference. For an ordinary unit-based scalar quantity, Q={Q}[Q], where {Q} is its numerical value in unit [Q]. Thus 5.34m and534cm express the same length with different numbers. Not every reference is a unit: specified procedures or reference materials can also define how a value is expressed.
Values and equations
Q={Q}[Q]
- Q
- Quantity expressed by a number and a chosen unit chosen quantity unit
- {Q}
- Numerical value relative to that chosen unit 1
- [Q]
- Chosen measurement unit chosen quantity unit
Conditions and scope
- The algebraic notation is for unit-based scalar quantities; non-scalar or ordinal values require their stated representation.
- A unit conversion changes the numerical value, not the underlying quantity; a procedure-defined reference requires its own interpretation.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- International Vocabulary of Metrology (VIM3)Joint Committee for Guides in Metrology (JCGM)Reference guideVIM3, entry 1.19VIM3, entry 1.20
Evidence and review
Read VIM1.19 definition/notes and Example1, which gives5.34m/534cm; VIM1.20 supplies the numerical-value definition and Q/[Q] notation, with its separate5.7kg/5700g example. The displayed conventional notation restates the ordinary number-times-unit case rather than treating all measurement references as physical units.
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Entry details
Permanent link to this entry ↗- Record identity
- foundation-measurement-value-number-unit
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions