The combination of a value and unit is known as a measurement. In the units library they are constructed by multiplying or dividing a unit by a numerical value.

measurement meas=10.0*m;
measurement meas2=5.3/s;

They can also be constructed via the constructor

measurement meas(10.0, kg);
measurement meas2(2.7, MW);

There are two kinds of measurements the regular measurement which uses a double precision floating point for the value and a precise_measurement which uses a double and a precise_unit. In terms of size the measurement class is 16 Bytes and the precise_measurement is 24 bytes.

Precise measurements

A precise measurement includes a double for the value and a precise_unit to represent the unit. Most of the string conversion routines to measurement produce a precise_measurement. the measurement_cast operation will convert a precise_measurement into a regular measurements.

precise_measurement mp(10.0, precise::kg);
measurement meas2=measurement_cast(mp);