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Numbers, units and symbols

Please provide a sample calculation. All constant and variable symbols should be defined consistently, and should conform to industry norms where possible.

Numbers 10 and above should appear as numerals except where the context makes this awkward, such as at the beginning of a sentence:

  • ‘There were 10,000 people in the town.’
    • but, ‘Ten thousand people were in the town.’

In text, all numbers lower than 10 should be spelled out as words, except where attached to a unit or percentage:

  • three houses
    • but: 3 mm
    • 3 kg
    • 3%.

Introduce a comma into numbers larger than four digits:

  • 4000
    • but 40,000.

CIBSE publications use SI units. A full list can be found here:
International System of units – Wikipedia page

This list of physical quantities may also be helpful:
List of physical quantities used in SI units – Wikipedia page

Do not italicise units or functions (such as summation sign or delta). Subscripts are generally not italicised (there are exceptions, such as i and j when associated with a summation sign).

There must always be a space between a number and its unit – though not for percentages (as this is not technically a unit):

  • 10 cm
  • 10 kW
  • 10 °C
    • But 10%.

Please separate compound units with a dot, preferably a midline dot:

  • kW·h

(The ‘midline dot’ symbol can usually be found in your program’s ‘advanced symbols’ list.)

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