I use old fashioned pen and paper because it allows me to write what I want about each dive.
Depending on the dive, there are different things I write about each one. Sometimes I write about where I was, what I saw, and who I was with. Sometimes I write about tasks or skills I practiced or attempted. Often I write about stuff I did wrong. So it's part diary, part reference, part confessional, part reminders and resolutions.
Sometimes I write about lessons learned. For example, last week I conducted a search in zero vis for the rudder that fell off a friend's boat. Even though we didn't find it, I think we executed the search very well. My lesson learned pertained to turning up the brightness and reviewing alarm parameters on my computers before low vis dives because during the hour-plus that I was crawling through lake muck in expanding circles with a metal detector, I couldn't read anything on either of my computers. One of them has the PSI numbers turn to red when you get low on air, but I didn't remember the threshold, and didn't know when the audible alarm would sound. I could barely discern that the numbers hadn't turned red yet, but other than that, I didn't have any information on my air consumption or anything else pertaining to the dive.
I refer back to it often, especially when deciding what to wear and how much weight to use.
