5 Quantities library [qties]

5.8 Types [qty.types]

5.8.1 General [qty.types.general]

A quantity type is a type Q that is a specialization of quantity or quantity_point.
Q represents a quantity (IEC 60050, 112-01-01) with Q​::​rep as its number and Q​::​reference as its reference.
Q is a structural type (N4971, [temp.param]) if Q​::​rep is a structural type.
Each class template defined in subclause [qty.types] has data members and special members specified below, and has no base classes or members other than those specified.