The GA100 is G-Shock's most popular analog-digital watch, and setting it confuses people because the hands and the digital display are set separately in the owner's head but not in the watch: set the digital time and the hands follow. This guide covers setting the time, DST and city, aligning the hands if they drift, and the alarm and world-time basics on module 5081 (GA100, GA100MB, GA110 and their color variants).
Buttons
On every G-Shock the four buttons are named the same way: A is top-left (Adjust), B top-right, C bottom-left (Mode), D bottom-right. Your watch's module number is engraved on the case back; Casio's manual for that module is the final word.
Set the time
- In timekeeping, hold A (top-left) about two seconds until the city code flashes.
- Press D or B to pick your city (NYC, CHI, DEN, LAX for the U.S. zones).
- Press C to move to DST; set AUTO or ON/OFF with D.
- Keep pressing C: 12/24-hour → seconds (D resets to 00) → hour → minutes → year → month → day.
- Press A to save. The hands move to match the digital time.
Fix the hands if they are off
If the hands do not match the digital display, after a drop or a battery change: in timekeeping, hold A for about five seconds until H.SET appears and the hands go to 12:00. If they stop short of 12, use D (clockwise) and B (counter-clockwise) to line them up exactly, then press A. The watch resets the hands to the current time.
Alarm
Press C until the alarm screen (AL) shows. Hold A until the hour flashes, set hour and minutes with D/B and C to move, press A. Press D on the alarm screen to turn the alarm on or off; SIG turns the hourly chime on.
World time
Press C to the world-time screen (WT). D cycles cities; hold A and press D to toggle DST for that city.
Backlight
Press B in any mode. Hold B in timekeeping to toggle the auto-light (the watch lights when you tilt your wrist).
Which GA100 is this
The GA100MB-1A (matte black, green accents) and the GA110MB-1A X-Large share module 5081 and these steps. The GA010 is the newer analog-digital with the same button logic.
Frequently asked questions
How do I set the time on a G-Shock GA100?
Hold A until the city flashes, pick the city with D, press C through DST, 12/24, seconds, hour, minutes, date, then press A.
How do I set the hands on a GA100?
Hold A about five seconds until H.SET appears, align the hands to 12:00 with D and B, press A.
Why are my GA100 hands wrong but the digital time right?
The hands lost their home position. Run the H.SET correction above.
How do I turn off the hourly chime?
On the alarm screen, press D until SIG is off.
What module is the GA100?
5081.
The bottom line
Hold A, city, DST, then the fields in order; H.SET if the hands drift. Buy the GA100MB-1A if you want the watch this guide is written on.
Related reading
How to set the time on any G-Shock
G-Shock GA100MB-1A review
Best G-Shock for EDC
