How do you make a dive computer?

Actually it is very easy. You only need a depth gauge, a timer, decompression tables (such as the RDP) and a brain:). You must also figure out how to carry all these instruments - my forearm is too short, especially when I also take a compass and a slate... The picture below shows the equation for a dive computer.

The first thing is my depth gauge. It's a capillary one, it consists of a tube open at one end and a scale. You read the depth by checking where the water that's in the tube ends. This particular gauge is 20+ years old, got it from my uncle (the same who found the SCUBA unit). My watch is Timex Ironman, its 200m water resistant (watches must be at least 100m water resistant), and has a timer. The deco table is, obviously, the PADI RDP. These items sum to a dive computer, in the picture you can see a Suunto Vyper that Magda got for Christmas.

Diving with such a dive computer makes you a more conscious diver, however recalculating your No Decompression Limit underwater is more error prone. It's also impossible to get a detailed dive profile, the water temperature etc. That's why the next piece of diving equipment I'm going to buy is a diving computer, probably the Vyper.