Here is my classic 1980s (from 1984 this model) Casio that takes me back to my school days. This watch came in a job lot and I have learned to examine very carefully these little circuit boards as it does not take much muck to stop them from working. I cleaned this 3 or more times and it would only work when it got warm by leaving it in my pocket ( a little trick I have learnt) turned out there was a little sticky gunk between the contacts of the quartz crystal. Once cleaned off its not stopped running since.
Nice basic model. No functions other than whats on the screen. No light or chono. Its also very thin. It is however a steel case rather than chrome plated which is a nice touch from Casios like this today.
Edit…. well it did stop after about 12 months and I can now only get it working intermittently. I have a potential donor module to fit when I get around to it.