You don't have to do math at depth, just write down your time at ascent, the math happens at the first decompression stops and you should know roughly what the deco profile will look like before you get in the water, especially when you're in the ocean with nice square profiles
I hear ya. I'm not saying the math is hard. I'm saying that looking at a computer (or even two computers) is easier. It's less of a task load. Maybe a non-issue if the dive is/has been going well. If the dive has gone awry, maybe an important difference?
I like math. I majored in math in college. It's not like I avoid it because I don't like it or am lazy. I sometimes solve quadratic equations in my head to occupy my time. But I also do what I can to minimize or streamline all tasks that I would ever have to accomplish while I'm underwater. With redundant capability where it makes sense and is feasible. Computer or mental arithmetic. It's all just a way of calculating an ascent plan, right? That task seems smaller and more streamlined if I can accomplish it by looking at 2 computers and mentally verifying that they are both saying pretty close to the same thing. Even better if I have the spare tasking capacity to do so and find that the dive computer solution compares appropriately with the plan I worked out ahead of time using Multi-Deco on my laptop (or similar).