Dive Computers

[DRE]

Beeger explained quite well what I meant. To give you an example: a lot of divers will do 4 dives per day for a week when they're on a liveaboard. At the end of the week they'll have a manifestation of DCS, although they never ascended too fast, never even went into deco according to their computer and even were using nitrox.
DAN labels that as an undeserved hit. Now, most people do their deepest dive first. When they come up from dive 1, some of the bubble nuclei that never were completely compressed during descent are still present in the blood stream. On dive 2 this diver does a shallower dive. The bubbles still present in the bloodstream from dive 1 start accumulating more inert gas. The deco obligation for dive 2 is less according to the computer since it is a shallower dive, but the bubble present doesn't follow this schedule. Now repeat this scenario over and over and you get an undeserved hit. Take into account that 25% of the population also has Patent Foramen Ovale and this probably explains 90% of all so-called undeserved hits.
If you know this, you get checked for a PFO and do your deepest dives last, so all the bubbles present can recompress, and you can do a proper ascent and stops and you won't get hit.
As far as computers are concerned, most give you way too much deco because they are not designed as a deco computer (the equivalent of the PADI tables), or they do give you somewhat of a proper shape and time, but then they're hugely expensive and not worth the money anyway since a bottom timer and tables do the job just as well. If you want to carry a backup, a second bottom timer isn't a bad idea, although your backup bottom timer should be your buddy's.
The 1200$ that it costs to buy a VR3 can be spent on a set of doubles, an HID canister light and a bottom timer. I know what to spend my money on.
Also, a diver constantly relying on his/her computer to get the job done will eventually become overly dependent on the unit - which can only lead to some degree of a disaster when the sh*t really hits the fan.