My Oceanic DataMax Pro+ 2 Air integrated computer has a feature called air time remaining, and when I first descend that is what is controlling my dive time. It displays the lesser of whatever is controlling dive time: air, no deco, O2. Below is also a bar graph that shows estimated gas time remaining throughout the dive even when the main display is showing other data.
Often on descent I am panting from the exertion of gearing up and excitement of getting in and it will show a really short time left for my gas, so I glance at it and slow my breathing and suddenly that time expands greatly. It’s like biofeedback and a reward for breathing calmly. I find this feature really helps me to slow down and breathe better, maybe something like this would be a good feature for you in your dive computer. This is an older computer and is available for a lot less than a newer computer that would have the same features, however it does have a very aggressive algorithm. If money is no object, or if you plan to advance into technical diving, everyone is going to tell you to get a Shearwater.
