Really the percentage sign just denotes a centi-1. Just like a centi-meter is 1 hundreths of the unit 'a meter', a percentage is 1 hundreths of the a (unitless)

Really the percentage sign just denotes a centi-1. Just like a centi-meter is 1 hundreths of the unit 'a meter', a percentage is 1 hundreths of the a (unitless) unit '1'.