I remember reading somewhere that if a unit is abbreviated as one character, there must not be a space between the number and the unit. For example 5m, 26K etc. If the unit is abbreviated as two or more Characters, there must be a space between the number and the unit. For example 10 kms, USD 5 etc.

1. Can you please help me find the source again?
2. Is this recommendation correct?

I remember reading somewhere that if a unit is abbreviated as one character, there must not be a space between the number and the unit (e.g., 5m, 26K). If the unit is abbreviated as two or more Characters, there must be a space between the number and the unit (e.g., "10 km", "USD 5").

• Can you please help me find the source again?
• Is this recommendation correct?