I am having a hard time learning the PADI dive tables. There seems to be nothing intuitive about it, as it is just an arbitrary construct. Is there any material on the web that offers a useful explanation regarding how to learn to use it?
I'll take your question in it's
literal extreme.
Such similar style "calculators" were very common in engineering for many years. Also in engineering, we see circular computers that are very mission specific.
Simple wheel devices were used by graphic artists to compute what % of image reduction you will need to make a 16" picture into a 10" picture.
Cubic Yards of concrete had similar devices. There must have been hundreds of different such gizmos.
Before electronic calculators, we all learned how to do math on
slide rules (slip sticks). Slide Rules were very expensive highly machined metallic instruments that served only to align finely printed numbers on moving surfaces. (You could look at a PADI wheel and describe it that way)
That PADI
wheel is also an invention that arrived a bit too late to be of any real use. Much derided as it is, it still is a mechanical visual demonstration of how multi-level diving can affect your diving.
Remember, the standard
card tables only take into account your maximum depth and figure everything from there. This was because they were derived from sending healthy young fat-free Navy divers to a pre-set depth, working on a project, then hauling them back up. There was simply no need or research in "multi-level" diving, dives where you go up and down and poking around. We started dive manuals for civilian use by utilizing Navy tables. It was all we had.
As an electronic calculator is to math, The eRDP is to dive tables.
Your dive computer has these dive tables in its brain, and it has also been taught to interpret your depth moment by moment and extrapolate for those known numbers.
Learning
how the tables work is integral to your understanding of Nitrogen loading. Learning to work the tables is a different deal.