Casio G-Shock watch movements or calibers are called modules. It sounds fancy, but when you read that a specific GShock watch model has a certain module, they are talking about the movement inside. These modules are essentially just digital (and sometimes ana-digi) quartz movements.
Some of the topics covered in this caliber listing:
How to find the module number?
The module number can be found on the caseback of your G-Shock watch. Look for the 4 digit numeric code with a box around it.
List of G-Shock Modules:
On this page, the G-Shock modules will be listed in groups. This can make it easy to find what battery your watch calls for, or if certain modules are interchangeable. Each module will be linked to the caliber listing. If there isn’t a caliber listing yet, it will be linked to the Casio G-Shock official watch manual archives.
If you have a GShock not listed here, please comment below.