How to Check a Metronome
Obviously, to check a metronome the first requirement is an accurate standard. Perhaps the most accurate standard commonly available when this treatise was first published, was the electric clock with a sweep second hand, which runs on an A.C. (Alternating Current) electricity supply. Even more accurate is a quartz electronic wristwatch with a stop-watch feature.
Some musicians check their metronome at 60 because it is easy to do so. Accurate operation at 60 does not imply accuracy throughout the scale. Metronomes should be checked at not less than four points, say 40, 60, 120 and 208.
In checking a metronome, the common and correct method is to count 1,2,3,4,5 and so on with its beats, for a period of one minute and compare the count with the metronome setting. However a warning is necessary. When the clock hand crosses the starting line and the metronome beats, do not count "1." At this instant, count "zero," or "start." The next beat is 1. This is because the final count is made when the hand again crosses the starting line. Counting beats both times would erroneously add a beat to the correct speed. This detail has been explained at length because it differs from the counting of musicians who have been trained to count by numbering the beginning of each interval.
When the error is 1% or less at all settings the instrument is highly accurate. If the error runs to 3% at some settings the accuracy is fair. If the error is 5 to 10% at any setting the instrument is very poor. If the error is 10 to 15% at any setting the instrument is worthless as a standard of tempo.
There is no way to check uniformity of beat without a chronograph. However, some instruments are so lacking in uniformity that an untrained ear can detect a "limp," or a sporadic irregularity. Such instruments should be exchanged for good ones. Uniformity is seldom an issue with quartz electronic metronomes. Keywound metronomes are most often prone to "limping".
A metronome may be uniform and not accurate. That is, the instrument may be so uniform that precisely the same time interval elapses between any successive beats, yet instead of beating say 104 when set there, it may beat 112 or 96. Such an instrument would not be useful for the work described in this Chapter. However, it would still be useful for the work described in Chapter II.
A metronome cannot be non-uniform and accurate. if the time between heats is irregular the number of beats per minute is only an average.