Often in TNG (especially later seasons), PADDs seem to have a subtle convexity to them.
I'm assuming this was intentional, and it means simple layered cut acrylic wouldn't fit the bill. I'm wondering if anyone has heard how this was accomplished (or perhaps @hms can enlighten us directly). One way might be to take a cut-acrylic master, warm it in a toaster oven, and then lay it over a wooden curved jig. This could then be used to make a mold.
I'm not really looking to make one myself; I'm just kind of curious about the process. It's a very interesting little detail that would introduce a surprising amount of additional manufacturing effort for something that is so slightly perceptible, so I guess it's also possible that it was the result of some kind of happy accident.
Anyway, it's something about which I've always wondered and would love to know more.