SMM12 — Description of RescaledMeasurement class is too restrictive

The description of Sub-clause 15.3 (RescaledMeasurement Class) begins with:

The RescaledMeasurement class represents the measurement results of applying to the base measurement the operation specified by the Measure to rescale the measurement.

A RescaleMeasure may have a multiplier and offset specified and not have an operation. This opening sentence needs to be generalized to include multiplier and offset.
Moveover, the first paragraph of Sub-clause 15.3 (RescaledMeasurement Class) suggests that a Rescaled Measure does always convert the Unit of Measure. This assumption is too strict as well.

Relax restrictive description

The restrictions as suggested by the descriptions, as referred to in the issue's Description, will be relaxed.