Interval Timer
Work and rest in sequence — Tabata, HIIT, EMOM, circuits, stretching, Pomodoro. It keeps time from the clock rather than by counting ticks, so it stays accurate when the tab is in the background, and it beeps on time even while you are in another app.
Why the timing holds up
Most timers in a browser count seconds by adding up interval callbacks. Browsers throttle those callbacks to roughly one a minute once a tab is in the background, so a ten‑minute timer left behind a another tab finishes late — sometimes by minutes — and there is no warning that it happened.
This one never counts. It records the moment the session started and works out where you are from the current time whenever it draws, so a display that went stale while you were away is correct the instant you come back. The beeps are handled separately: every cue for the whole session is scheduled on the audio clock in advance, which browsers do not throttle, so they sound on time even while the tab is hidden.
Where the presets come from
Tabata is the most specific and the most often misused. It comes from a 1996 study by Izumi Tabata and
colleagues, and the protocol tested was twenty seconds of work at a very high intensity followed by ten
seconds of rest, repeated eight times — four minutes in total. The interval structure is the part
people copy; the intensity is the part that made it interesting, and without it the four minutes are just
four minutes. Anything using a different work-to-rest structure is an interval workout, which is fine,
but it is not the thing that was studied.
EMOM — every minute on the minute — inverts the design. The interval is fixed and the rest
is whatever you have left after finishing the work, so the faster you work the longer you recover. That
makes it self-scaling, and it also means a badly chosen workload turns the rest to nothing without the
timer noticing.
A circuit is simply a sequence of different intervals with a longer break between rounds. It is the
most general shape here, and the one worth building yourself rather than taking from a preset.
What a timer can and cannot tell you
This is a clock with a schedule attached. It counts intervals and it makes a noise at the boundaries.
It has no idea what you are doing, how hard it is, or whether you should be doing it, and nothing in the
presets is a recommendation about your training or your health — they are the published structures,
reproduced so you do not have to set them up by hand. Whether a given protocol suits you is a question
for someone who knows your circumstances.
