If I plan a dive outside rec limits I use a software planner. My trusty Vyper is usually more conservative than that, so I tend to follow it, but if it ever craps out, I have my plan to finish up with.Al Mialkovsky once bubbled...
I really didn't trust the computer at first so I always did the plan with the wheel. Of course if you're in an interesting area it's easy to screw the plan up anyway. So the faithful computer is there to save your butt.
I dive with two computers of the same make and model.
If I'm doing a "recreational limits" dive, I always know if my computer crashes, slow ascent with 3 min @ 20, 3 min @10 *should* keep me unbent....