To provide the best possible stability, the metronome is implemented using sound files that must be loaded when a tempo is selected. Once loaded, the tempo is cached by the browser so it can be selected instantly until the cache gets cleared (page refresh, etc.).
A "Repeat" checkbox is provided to continuously alternate between 2 minute drills and 15 second breaks.
Background image by Pauline Moss. at http://paulinemoss.deviantart.com/art/Stars-307119758