I would suggest you turn recalculate off completely. Before doing this I had no end of problems.
If you are following a course and things go wrong or you forgot to turn on prompts, you can always start the course again. Very occasionally I find the turn by turn instructions go wrong and restarting the course fixes it. The unit will still be recording fine.
I would also suggest you take a look at bikehike.co.uk. This allows you to load the track direct to the 800.
A single press of the power button should bring up a screen that allows you to adjust brightness and also to lock the unit. Turning off requires a longer press
If you are following a course and things go wrong or you forgot to turn on prompts, you can always start the course again. Very occasionally I find the turn by turn instructions go wrong and restarting the course fixes it. The unit will still be recording fine.
I would also suggest you take a look at bikehike.co.uk. This allows you to load the track direct to the 800.
A single press of the power button should bring up a screen that allows you to adjust brightness and also to lock the unit. Turning off requires a longer press