My plan is to keep the user interface minimal — only a thumbwheel for zoom, and two switches: on/off and backlight on/off (turning the backlight off will save a lot of power and switch the display to sunlight-readable mode).

I also want to make the PiChart as waterproof as possible. I need to be able to navigate in the rain! I want to keep the front side, which will probably be most exposed to the rain, sealed. But I also want the switches easily accessible.

So one idea I want to explore is to make a brass lever, attached like a dial indicator at one end that it can rotate around. Stops would let the user flip the dial from one position to another (say from 2 o'clock to 4 o'clock positions). On the other end, I'd attach a magnet. The magnet would keep the dial attached to one of the endstops when the user is not moving it.

Under where the magnet ends up at one of the endstops, I'd have a reed switch that toggles from the magnetic field when the dial is above it.

I have not used reed switches before, but it seems like a fairly simple way to make a custom, attractive, waterproof switch solution. Also, the reed switches don't need to be powered as Hall sensors do, so when the device is off, it can be completely turned off.

I've ordered reed switches from Ebay and will report back when I've done some tests. I'm unsure how big magnets I need, and what the distance can be between the magnet and the reed switch.