Flip your watch over and look at the engraved text on the metal case back.

The GN-4W-S-12G typically features a 24-hour sub-dial at the 9 o'clock position. It is slaved to the main hour hand. If you set the main time correctly, the 24-hour hand will automatically show AM (0-12) vs. PM (12-24).

To find the correct manual for your Citizen Eco-Drive GN-4W-S-12G , you need to identify the movement caliber