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On Apple Watch

One control, and it is not Start

Getting into water begins a round on an Apple Watch Ultra, any generation, or a Series 10 and later — the models with a water temperature sensor. Every other Apple Watch runs the same app with each round picked by hand.

The constraint that shapes everything

Water Lock comes on when you get in, so a splash cannot tap the screen. For the length of the round you are not going to be operating the watch, which means the app cannot need you to. Every automatic behaviour follows from that: the round that starts on submersion, the round that closes when you climb out, the prompt whose default answer is correct, and the session that ends itself once you have plainly stopped.

The one thing a person has to do is get in the water.

  1. The first watch page during a plunge: a round clock reading 4:05 in cyan, the label PLUNGE ROUND 4, In water at the top right, a heart rate of 126 with a round average of 124, a water temperature of 48.4 °F, and a Switch button
    Page 1

    The round

    The round clock, level with the system clock. Heart rate with the round average beside it, the water reading, and one control. Readiness sits under the system clock at the far end.

  2. The second watch page: total time 25:05 and round time 4:05 at the top, then current heart rate 126, average 124, minimum 121 and maximum 126
    Page 2

    Heart rate

    Current, average, minimum and maximum for the round in progress. Turn the Crown to change the scope from the round to the phase or the whole session.

  3. The third watch page: total and round time at the top, then current water temperature, average, minimum and maximum
    Page 3

    Water

    What the sensor is reading now, and the round’s average, minimum and maximum. On a sauna round this falls back to the last soak, dimmed and labelled as such.

  4. The fourth watch page: total time 25:05 and round time 4:05, then hot 17:05, cold 3:00, rest 5:00, 4 rounds and an average heart rate of 100
    Page 4

    Totals

    Hot against cold against rest, the round count, and the session’s average heart rate. Rest is a timed segment, so it has a total of its own.

  5. The watch during a sauna round: 4:35 in red, SAUNA ROUND 4, heart rate 118 with a round average of 114, and a last bath reading of 106.2 in a dimmed colour
    —

    A sauna round

    A sauna is dry, so there is nothing for the sensor to read. The water row shows your last soak instead, in a dimmed colour, clearly labelled.

Seven case sizes, one rule

Numeral sizes are derived from the screen rather than typed:min(height × 0.145, width × 0.172), with the caption at 37% of that. A 40mm case gets about 28pt and a 49mm Ultra about 36pt, from the same line of code.

Two things own parts of the screen and the layout works around both. The system clock owns the top-right band, so the first number on every page sits level with it and nothing runs underneath. The page dots own the right edge, so content stops short of it.

Supported: 40, 41, 42, 44, 45, 46 and 49 mm.

Ending, and forgetting to end

Lift your wrist out and the watch asks out of water? with a 30-second countdown. Either answer closes the round at the moment you actually left the water rather than at the moment you replied — so ignoring the question is a valid way to use it.

Walk off entirely and the session closes itself after five minutes of rest, adjustable from one minute to three hours, with the end back-dated to when you stopped. A single round past 90 minutes closes too. A forgotten session records the duration you did, not the afternoon you had.

How auto-end works →