Casio watches typically feature a module number (also called a caliber number) on the case back, which is often a four-digit number identifying the electronic module inside the watch. This module number is commonly the most useful identifier, as it can be used to access Casio's online manual database to find the complete user manual and specifications for the watch. The module number is typically displayed prominently on the case back, often alongside or near the model reference.
The model reference number, which more specifically identifies the watch's design and variant, is also commonly found on the case back. For G-Shock watches, model numbers typically follow formats like 'DW-5600E' or 'GA-2100-1A1', where the letters indicate the series, the numbers identify the specific model, and the suffix indicates the color or variant. This model number can usually be looked up on Casio's website or in collector databases to identify the exact watch.
Casio watches may also feature a serial number for warranty and tracking purposes, though the serial number format and location can vary. Unlike some traditional watch brands, the serial number on a Casio watch is generally less useful for dating purposes, as the module number and model reference are typically more informative. For production date information, the date code stamped on the case back or printed on the battery compartment label can sometimes indicate the manufacture date.