How should a numerical value be expressed?

ISO 80000 specifies the following rules on how to express a numerical value of a physical quantity:

Sign - Positive or negative sign should be placed immediately before the number without any space. For example: -1.

Grouping - A number with many digits can be separated into groups of 3 digits by a small space. Groups must be started from the decimal point. For example: 1 234.567 8.

Scaling - A large number or small number can be scaled with an exponential expression. For example: 6.62607015 × 10⁻³⁴.

Rounding - By default, a number is assumed to be rounded to the last digit in the expression. For example: π = 3.1415927 means that the value is rounded to 7th digit after the decimal point.

When rounding occurs before the decimal point, it should be scaled with an exponential expression. For example: the temperature at the sun's surface should be expressed as 5.5 × 10³ °C, not 5500 °C, because it is rounded to second digit 5.

Uncertainty - By default, the uncertainty of a numerical value is assumed to be within the rounding range of its expression. If the uncertainty is larger than the rounding range, it can be expressed in terms of the last digit of the numerical value and place it in parentheses immediately after the last digit.

For example: d = 23.4782(32) m indicates that this distance has an uncertainty of 0.0032 m.

⇒ ISO 80000-2 Quantities and Units - Mathematics

⇐ Quantity Equation in Coherent Units

⇑ ISO/IEC 80000 - Quantities and units

⇑⇑ MathML (Mathematical Markup Language)