Number

A basic SI number is a float, such as 12345.67891. The decimal marker can also be a comma, such as 12345,67891. For readable, a thin space is also allowed, such as 12 345.678 91. Exponentiation is specified with the superscipt numbers; 3² is equivalent to 9.

A precentage is specified with the percent sign. 0.25 % is equivalent to 0.0025.

An uncertain value is specified with the left parenthesis and right parenthesis symbols, such as 12 345.678 91(5) and is equivalent to 12345.67891±0.00005.

Multiplication is specified with the multiplication sign, such as 1.234 567 891(5) × 10⁴ and is equivalent to 12 345.678 91 ± 0.000 05.

ASCII Number

The SI representation of a number requires Unicode code points outside of the ASCII characters. To make life easier for programmers the following relaxations are allowed:

• Any white space character can be used for a thin space
• * can be used for a multiplication sign
• ^ or ** can be use for exponentiation

For example, 1.234 567 891(5) * 10**4 is equivalent to 12345.67891±0.00005

Quantity

A SI Quantity consists of a number and a unit. If not specified, the number defaults to 1. The unit is a defined ISO-80000 symbol or a symbolic expression.

Any of the following expressions can be used to define watt per square metre steradian:

• W/(m² sr)
• m² m⁻² kg s⁻³
• kg s⁻³