How it works
A 138 metronome plays the speed Beethoven asked for in the opening movement of his Piano Sonata No. 29, Op. 106: half note = 138. Wikipedia's article on the sonata traces the mark to a letter of 16 April 1819.
Read the full guide
Start
Tap the pad, or press Space, and the metronome click at 138 begins. Set against that movement, one click is one half note. Tap a second time to stop.
Change the tempo
Tap the number under the pad and type a tempo, or use minus and plus. Typed as 276, twice 138, the same speed is counted in quarter notes.
Questions and answers
Is half note = 138 too fast for the sonata?
Performers have often thought so. Wikipedia's article on it says they regularly set the figure aside, blaming a slip by the composer or a metronome that ran wrong. It also reports the opposite case: that such a tempo was a standard Allegro in the 1780s.
Is half note = 138 the composer's own mark?
Yes. Wikipedia's article on the sonata says Op. 106 is the one piano sonata Beethoven supplied with metronome marks. The metronome was patented in 1815, four years before the letter, and the article counts him among the earliest composers to take it up.
Is 138 BPM the middle of allegro?
Yes, to the beat, in Wikipedia's list of tempo markings: Allegro spans 120 to 156, and 138 stands 18 from either end. Molto allegro, 124 to 156, holds it too. The sonata's movement is marked Allegro, though its 138 counts half notes.
Are 138 and 144 next to each other on a metronome?
They are on the most common wind-up scale. Wikipedia's Metronome article sets out a short run of sixes, 126, 132, 138 and 144, between the fours that finish at 120 and the eights that begin with 152. So 138 has a notch of its own.
Why can't I hear the metronome?
Silence on a phone tends to have one of three causes: a ring switch flipped to silent, a volume slider at its lowest, or a Bluetooth device that has claimed the click. Either way the pad's two dots go on changing over, beat by beat.