I've bought a few Casio F91-W watches, a few pluto PCBs and the parts that go with them.
The goal is to assemble all of this and get a functioning watch with some features out of it. For this, I've still got to find out how exactly I'm going to solder these tiny SMD components.
I'd love to use a Casio W86 for this, as it is rated to be waterproof until 5bar and has an "illuminator" display, meaning the whole screen is illuminated so you can actually read the digits in the dark easily. Problematic: they cost about double the price of a normal F91w and probably won't retain the 5bar waterproof rating (they won't and the f91w doesn't even start with such a rating, but it would be kind of bad to ruin an otherwise perfect watch for this).