TS 1990 ISO 31-0

TS 1990 ISO 31-0 is a standard on the general principles for physical quantities, their representation in equations, and the consistent use of quantity and unit symbols, with particular reference to the International System of Units (SI). Rather than defining a measurement method, it establishes the notation framework that helps technical and scientific documents present quantities and units in a uniform way.

How quantities and symbols are organised

In general technical usage, a physical quantity is any measurable property that can be expressed numerically, such as length, mass, time, or temperature. Units provide the reference scale for expressing those values. The key concern of this standard is the disciplined use of quantity symbols and unit symbols so they remain distinct, readable, and mathematically consistent in formulas and technical text. That consistency reduces ambiguity when equations are copied, compared, or translated across disciplines.

The SI context and coherent unit systems

The standard gives general information about SI and places coherent unit systems at the centre of the notation rules. In general technical terms, a coherent system is one in which derived units follow directly from base units without extra numerical factors. This makes calculations cleaner and helps show the physical relationships more transparently. The document therefore supports a common language for quantities and units, while not prescribing a specific laboratory test or an application-specific procedure.

• General principles for physical quantities and their symbolic representation
• Consistent use of quantity and unit symbols in equations
• General information focused especially on SI
• The concept of coherent unit systems and notation discipline