This convsersation makes me imagine what it was like for Doctors 50 years ago when someone introduced them to a defibrillator for the first time!!! I am a DM and regularly work on charter boats. It seems like once or twice a month, we'll get some old salt on-board... you know, the one who has been diving since 1941??? Anyway, there starts the conversation about computers... and how the old timers never used those silly things. Newsflash people!!! it's called technology... just like Doctors getting new and better toys, so do divers. With regard to the bottom time issue, you should know your approx max depth before you begin the dive or you should not be doing the dive... so the point from Bubbleblower about all the computer users staring at NDL and not max depth is a mute point. Your NDL is far more important than your max depth!!! Your max depth means nothing as far as potential DCS if you don't take into consideration how long you were at that depth... which takes us full circle back to what a computer does for you... it calculates an algorythem based on a combinbation of depth and time. In this day and age, it is silly for any diver to not use a computer. I not only use one, I also have a back up. As far as someone having one computer and it fails, you do need to know the basic (including using tables) to know where your profile is.