for walking/hiking in a straight line. buzzes twice when deviating to the left and once when deviating to the right.

## Settings

Open the app's settings (gear icon) in the Pebble phone app:

- **Line coordinates**: paste from the KML (see above).
- **Buzz when off the line by**: default 5 m. Phone GPS wanders by 2 to 5 m,
  so 5 m gives a few false buzzes per 10 minutes; 8 m is calmer.
- **Repeat buzz every**: default 10 s. Repeats stop while you are already
  walking back towards the line.
- **Ignore GPS worse than**: default 20 m. Weaker fixes show "WEAK GPS" and
  never buzz.
- **Walk in reverse**: tick this if you walk from the path's last point to its
  first. Otherwise left and right are swapped.

You can also paste the coordinates into `BUILTIN_COORDS` at the top of
`src/pkjs/index.js` before building and skip the settings page.

## On the watch

- Top: ON LINE / LEFT / RIGHT, then the offset in metres.
- Middle: the vertical bar is the line, the dot is you, the ticks mark the
  alert threshold. Hollow dot = weak GPS.
- Bottom: metres to the end of the line and current GPS accuracy.
- Screen turns red (black on black-and-white watches) while you are off the line.
- SELECT: mute / unmute. UP: demo the "left" buzz. DOWN: demo the "right" buzz.
- "NO PHONE" means no update for 20 s. "ARRIVED" within 10 m of the end.

## Things to know

- The phone does the GPS work. Keep the app open on the watch, and give the
  Pebble phone app "Allow all the time" location permission on Android so it
  keeps working with the phone screen off. Exempt it from battery
  optimisation if updates stop.
- The offset is averaged over the last 3 GPS fixes, so it lags a few seconds.