Every current iPhone has a barometer. Offwind reads it whenever the app is running, so there is nothing to switch on.
The pressure alarm
When the pressure has fallen by 3 hPa or more within three hours, from its highest point in that time, Offwind raises Barometer falling. It does not wait for three hours of history: a 3 hPa fall in 90 minutes alarms at 90 minutes.
It is a warning: the banner is a solid fill and the beep sounds three times. Acknowledge or snooze it as any other alarm (see Answer an alarm). It clears once the fall is back under 2.5 hPa, so it does not keep sounding on and off at the limit.
The readings are smoothed over five minutes, so a slammed hatch or a gust does not set it off.
While recording
While the track is recording, Offwind saves the pressure with it once a minute, and a pressure alarm is marked on the track as Barometer alarm. The pressure is in the Baro column of the Expedition CSV export. See Export a recording.
Limits
- The phone reads the pressure where it is. In a closed cabin that is cabin pressure, which lags and can be offset by ventilation. Every alarm says so: the trend is an indication, not a ship's barometer.
- The 3 hPa in 3 hours limit is fixed.
- The alarm's words are in hPa, whatever Settings › Units › Pressure is set to.
- The Baro field on the Helm shows the boat's own barometer, when your instruments send one.