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Rules for writing SI units and symbols correctly sheet
3-mark answer frame

State any four rules for writing SI units and symbols, with an example of each.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Space. Leave a space between the number and the unit: 100 mg, not 100mg.
  2. 2 · No plural. Symbols do not take s: 10 kg, not 10 kgs.
  3. 3 · No full stop. Do not put a full stop after a symbol: 10 mg of salt, not 10 mg. of salt.
  4. 4 · Capitals. Units named after people have capital symbols (5 N, 30 J); other symbols are small (m, kg, s).
  5. 5 · Combined units. Leave a space between symbols: m s⁻¹, because ms means millisecond.
  6. 6 · Close. Following these rules means every reader reads a value the same way.

Scoring tip: Give each rule with a right and a wrong example; that is how the marking scheme checks it.