The terminology in the earliest instructions for metronome
use is more ambiguous than it initially appears. An analysis of relevant
historical texts reveals that measure refers either to the allotment of time
between two bar lines or is used to denote the mensuration of the bars
themselves, where it without exception denotes two beats. In principle, the
measurement of time was defined metrically, that is, with regard to two points
in time, which furthermore meant that the mensuration of note values
representing the movement of the measure was taken for granted to mean a double
beat: the up-and-down of a hand or the back-and-forth swing of a pendulum.
Early guidelines, thus, establishing the measurement of the progression of bars
with two beats, can be properly understood only if one infers that the minute—on which the metronome was based from the
beginning—could have referred to two minutes in time. The derived
conclusion is as simple as it is momentous: nineteenth century metronome
markings generally indicate a tempo that is half as fast as one would
customarily assume.