A unary scalar function of continuous time. Maps a time-quantity into another scalar quantity such as a temperature. For example, a quantity that denotes 'the temperature of the top of the Empire State Building' is a time-dependent-quantity since its value depends on the time.
(<=> (Time-Dependent-Quantity ?X) (And (Unary-Scalar-Function-Quantity ?X) (Continuous ?X) (Subclass-Of (Exact-Domain ?X) Time-Quantity)))