Ah yes, the Casio PAS400B, I've seen a few of those, they're very nice watches, I was considering one, but I went for my science teacher's recommendation instead.
That's also a good question, ecoli!
I usually wear it on the outside, mostly because my watch looks very odd when I wear it on the inside, as in, the watchband is sort of weird looking.
When I wear my analog I usually wear it on the inside so it doesn't get scratched as much as it does when I wear it on the outside.