Chrono mode is only meant for when you are NOT swimming (i.e. running, cycling etc). In this mode the accelerometer is not operational and it will not count laps.
If you are swimming just press start from the normal time of day screen, no need to use the mode button at all. You will see an icon with someone swimming it the top of the screen and Lap 0 will be on the top row of characters. It's only if you are running or cycling etc that you should select CHRONO first.
Turning On/Off etc
The simple way
Imagine you are swimming a non-stop 2000m.
From the normal time of day screen, press the start button to begin. Lap 0 will be displayed, swim, then hold down the start button for 2 seconds to stop. This will save the complete session. Whilst in swim mode you can use the UP button to change between Laps, strokes, distance, calories and efficiency
A more advanced session- Recording sets
Imagine you are swimming 10 sets of 200m with 20 seconds rest between each one.
From the normal time of day screen, press the start button to begin, swim your first set.
Press start again quickly when you finish the first set. A P will appear in the bottom left of the screen. This indicates the watch is paused.
The time for the last set will stay on the watch for 3 seconds then the paused time will be displayed.
Wait until you have taken your required rest, hit start again quickly, the P will disappear and it will start timing your next set.
Repeat as required then when you finish the last set hold the start button down for 2 seconds to finish recording. This will save the complete session and each set within it.
Note- The watch should be paused if you are doing drills or kick sets as it will not recognise you are swimming if your arms don't correspond to the recognised strokes.