Cycling states
Double-click (double-tap): advance 13m → 5m → RUN IN → JIA → NEG → 13m.
Double right-click: step back through the same order.

Starting a clock
The 13m clock first appears stopped at 13:00. A double-click on an unstarted clock starts it rather than moving on. The 5m call starts counting the moment you reach it.

Stop / start
Once a clock has been started, a single click (tap) stops it - black background, white outline, stop symbol - and another click restarts it from where it stopped.

Reset
Hold the right button for 1 second to reset just the clock that's showing: the 13m clock goes back to 13:00, the 5m clock back to 5:00, both stopped (double-click to start). The other clock is left as it was. Does nothing on RUN IN, JIA or NEG.

Adjusting time
Mouse wheel over a clock changes the minutes up/down and resets the seconds to :00.

Memory
The 13m and 5m clocks are remembered independently. Leaving a clock freezes it; coming back to it resumes it from exactly that value, until it has finished (reached 00:00), after which it comes back fresh.

ETD
The small time under the countdown is the local clock time the drop is due.

Symbols
A flashing climbing aeroplane shows on the right of the button while a clock is running and on RUN IN (labelled <5m during the 5-minute call). Once JIA is selected (jumpers in the air) it changes to a flashing parachutist. Nothing shows on NEG or while a clock is stopped.

Colours
Grey = NEG, dark red = 13m, orange = 5m, flashing salmon = RUN IN, flashing red = JIA, black = stopped.

All of this is saved locally; a page refresh carries on from where it was, with a running clock catching up the time it was away.