Safety
This is experimental equipment.
Everything on this site is hobbyist, DIY hardware. None of it is certified, none of it is life-support, and none of it has been tested to any standard beyond my own diving.
Don't blindly follow the navigator.
A Tern instrument gives you an estimate. It does not execute your dive plan, and it does not replace training, a compass, or your own judgement. It absolutely does not take the place of real training or certification. Sanity-check it constantly against depth contours and time: if you're headed to a wreck at 76 ft and you're at 120 ft six minutes in, you've erred somewhere. If the screen says keep going and you're at 250 ft with no wreck in sight, stop.
Technical diving is dangerous. This is hobbyist, DIY equipment with no warranty and no certification of any kind. You are responsible for your own dive.
The specifics
Not a substitute for training. Not a substitute for a compass, a reel, a line, or a plan. Not redundant life-support, and not to be relied upon as though it were. Every device here can fail — flood, brown out, lose its calibration, or simply be wrong — and your dive plan needs to survive that happening at the worst moment.
Each project page carries its own note about how that specific thing can mislead you. Read the one for whatever you're building before you get in the water with it.