'A space separates the number and the symbol, e.g. "2.21 kg", "7.3×102 m2", "22 °C" Exceptions are the symbols for plane angular degrees, minutes and seconds (°, ′ and ″), which are placed immediately after the number with no intervening space.'
The numerical value always precedes the unit, and a space is always used to separate
the unit from the number. Thus the value of the quantity is the product of the number
and the unit, the space being regarded as a multiplication sign (just as a space
between units implies multiplication). The only exceptions to this rule are for the unit
symbols for degree, minute, and second for plane angle, °, ′, and ″, respectively, for
which no space is left between the numerical value and the unit symbol.
This rule means that the symbol °C for the degree Celsius is preceded by a space
when one expresses values of Celsius temperature t.
The symbol used to separate the integral part of a number from its decimal part is
called the decimal marker. [. . .] the decimal marker “shall be either the point on the line or the comma on the line.” The decimal marker chosen should be that which is customary in the context concerned.