As I posted, I could tell you within 5 feet where my depth is at any time, but I don't STARE at my depth gauge constantly. I can also tell you within 100 psi of my air, but I don't stare at my pressure guage either.
I can tell you everything about the dive at any time during the dive and be reasonably accurate.
Where we differ is this, I'll let my computer remember things for me, I won't let it think for me.
It's not important to remember the exact minute the dive begins and ends. When my dive is finished, I don't want to be repeating in my head, "Dive time 54 minutes" as I get to the boat or shore. Once I'm there, I don't want to have to write it down immediately. I want to help my buddy, clean my equipment, and sit for a second and reflect on the dive.
The dive computer stores information for my dive log, and it stores it more accurately than I would remember, which helps me plan my next dives.
Xanthro