As I understand it, the general rule is that where the unit is derived from a person's name, eg. Volt, Ampere, Watt, Kelvin, etc. the upper case is used as the abbreviation.
As I understand it, the general rule is that where the unit is derived from a person's name, eg. Volt, Ampere, Watt, Kelvin, etc. the upper case is used as the abbreviation.
It is also the rule that when the unit is stated in full the word is not awarded an uppr-case initial letter. So it's volts, amperes, watts and kelvins.
As a rider, people get mixed up when a unit is not named after a person. You see times in mS intead of the correct ms.