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How to set up Casio G-Shock GA-100 (user manual, user guide)

Tags: Guides | Casio | Classic

8.4.2021 | 5 MIN | 23x comment

The GA 100 is the best-selling G Shock and it is produced in many colours.

Casio G-Shock GA-100

What are the features of the Casio G-Shock GA-100 and how can you switch between them?

The GA100 has 5 modes: local time, stopwatch (STW), countdown timer (TMR), world time (WT) and alarm (ALM). Switches between modes using the (MODE) button. From the last mode, you get back to the first. You can recognize the basic mode (TIME) by the three-letter abbreviation of the day in the right part of the display.

TIME >> STW >> TMR >> WT >> ALM

What do the status indicators mean?

At the top left of the watch display, four status indicators are displayed on a small circular display. Labels are marked (although they are quite hard-to-read on the watch):

  • AL - indicates alarm on/off.
  • SIG - indicates on/off of the clock sound signal. The watch beeps every hour.
  • A.LIGHT - indicates automatic lighting on/off. The light turns on automatically when the watch is tilted toward the face (the watch monitors the tilt angle).
  • SNZ - indicates Snooze alarm on/off (repeated alarm).
Casio G-shock GA100

How do I turn the automatic lighting on/off for the Casio GA-100?

To turn on the display light, press . Automatic lighting is activated and deactivated by holding down the for a longer time (3 seconds), but you must be in the basic TIME mode. You can tell if the auto light is on by the lower left status indicator (A.LIGHT). The automatic lighting deactivates itself every 6 hours.

How does a alarm/snooze work?

The watch has 4 regular alarm clocks and one recurring one. When the recurrent alarm sounds, you can interrupt it by pressing any key. But the alarm will continue to run in the background and start ringing again in 5 minutes. It is necessary to end the repeated alarm by turning it off directly in the alarm mode (this is not possible by pressing a single button). If this does not happen, the alarm will repeat every five minutes, but no more than 7 times. Then the automatic alarm will turn itself off.

Move the watch to alarm mode (ALM). You can now use the to switch between the individual alarms in this order:

AL1 >> AL2 >> AL3 >> AL4 >> SNZ >> SIG

Drive to SNZ (repeated alarm clock). Hold down the to set it. The time (alarm hour) starts flashing. Use and to set the alarm hour, then press . The minutes start flashing. Adjust again with and . Press to end the setting. A short press of the controls the activation / deactivation of the respective alarm clock.

How to set the time on the G Shock GA 100?

  1. Switch to the basic TIME mode (modes are switched with the ).
  2. Hold down until the time zone starts flashing.
  3. Use the and to select the desired value.
  4. The always moves to the setting of further data. You can gradually set:
    - time zone (home city)
    - DST (summer time on/off)
    - time format 12/24
    - seconds, minutes, hours
    - year, month, date
    - LT (lighting time)
  5. To end the setting, press the .


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How to calibrate hands of the Casio GA-100?

If the analog hands do not display the time shown on the digital display, the hands must be calibrated.

  1. Switch to the basic TIME mode (modes are switched with the ).
  2. Hold , H-SET will be displayed and SUB will start flashing (ie you are now calibrating the dial knob at position 12)
  3. Use the to calibrate the hands to position 12. Right, it must point up to position 12.
  4. Press the to switch to the minute and hour hand calibration. 0:00 flashes on the display and both hands move to position 12.
  5. Use and to calibrate the hands so that they both point to position 12
  6. Press to end the calibration.

How to enable/disable daylight saving time (DST)?

  1. Switch to the basic TIME mode (modes are switched with the ).
  2. Hold down until the time zone starts flashing.
  3. The always moves to the setting of further data. DST (daylight saving time) is set as the second parameter for the time zone.
  4. You can switch summer time on/off with the .
  5. To end the setting, press the .

If daylight saving time is switched on, the abbreviation DST is displayed to the left of the time in the basic mode (TIME).

How to turn on/off the hour sound signal?

  1. Switch to alarm mode. Switch the mode with the until you see ALM (as alarm, alarm clock) on the right display.
  2. With the you can now scroll between the four alarms, the Snooze alarm (SNZ) and the alarm setting (SIG). Press until SIG appears on the right.
  3. The abbreviation SIG (audible alarm) is either ON or OFF. To switch the status, press the .

How do I switch the time to a different time zone on the GA-100?

The watch has WORLD TIME mode. To move from the basic local time mode to world times, press the 3 times. The display briefly shows WT as World Time, and after a while, the abbreviation of the world city for which world time is displayed.

Use the to switch between world cities that represent different time zones.

Zkratky světových měst a časové zóny

Abbreviations of world cities and time zones

When you are in world time mode, the digital display will always show the time in the city you currently have selected. But the hands will always show your local time, depending on the local city, which is set in the basic mode.

Attention: two conditions must be met for world time to function properly. 1) You must have correctly entered your home cities - in the UK, enter LON as London, which is the same time zone. 2) You must have the local time set correctly. World time is calculated from these data.

How to switch local and world time?

Very useful if you are traveling to other time zones. For example, if you are flying between Ostrava and London, as your home city you probably have PAR set as Paris (MAD, ROM, BER, or STO is also correct) and in world times you have chosen LON (London), in which there is an hour less than in central Europe. Upon arrival in London, it would be nice if the analog hands showed London time. Of course, you can change the time zone to London in the settings, but it's also much more elegant.

Just press both the upper and buttons at the same time in world time mode. This will change the home and world city. London will be set as the home city and Paris, or our Czech time, will be set as the world city. After arriving back to the Czech Republic, simply double-click to switch times back.


Demetrio Montalvoago 567 days, respond
How can I change the hour (+,- 1 ) in summer or summer?
Agáta Vřeskáago 567 days
Take a look at part https://www.hodinky-365.com/blog/casio-gshock-ga100-user-manual#dst
Sikoago 519 days, respond
Thanks. Helpful. I solved my problem. Calibrated issue
Joséago 493 days, respond
How do I shift the hands of the watch in order to view the digital display?
Eliška Měrkováago 492 days
Unfortunately, it is not possible on this model.
Philago 439 days, respond
Which time zone for s.c. cant set my watch.
Dominik Hokago 439 days
Hello, try SCL or NYC (New York and Santiago).
Kobusago 408 days, respond
Hi Dominik Thanks for the blog post.. it is very useful. I'd like to know if it is possible to change the background of the digital display from dark light.. in other words, invert the digital display.. I find the dark background hard to see at night.. Thanks
Dominik Hokago 407 days
Hello Kobus, sorry, but it is not possible.
Paulago 385 days, respond
Recently had new battery put in my ga 100, watch in stuck in countdown timer mode. Any advise please
Agata Vreskaago 382 days
Unfortunately, I can't think of any advice other than trying to reset the watch again (by removing and inserting the battery). I honestly haven't come across this yet. Of course, it is possible to send it to an authorized Casio service.
Dedenago 352 days, respond
What is the OVER needle for ?
Nielago 328 days, respond
What city time zone to use in South Africa because Athens does not show the right time?
Dominik Hokago 326 days
Hello Niel, the best would be to set PAR (Paris) or BER (Berlin).
HermanMunsterago 230 days, respond
Terrible instructions - how are you supposed to know which button to push? It's not obvious.
Dominik Hokago 229 days
Hello, in the article you have a picture that shows the "labels" of the buttons. Then you just click the buttons according to the "labels".
Coleago 215 days, respond
How do I set my time given my country(Kenya) is not on the time zone
Agata Vreskaago 214 days
Hello, you can set a time zone that is +3 hours from UTC. So for example JED
Jeffago 201 days, respond
My analog hand is 10 minutes behind the digital time. How can I fix this?
Agata Vreskaago 200 days
Hello, Jeff. It is necessary to calibrate the hands, see https://www.hodinky-365.com/blog/casio-gshock-ga100-user-manual#kalibrace
Asad Ullahago 179 days, respond
The second hand at the top middle of the dial doesn’t move with the time . How to solve this issue
Filip Debrecenyiago 177 days
Hi Asad, normally it doesn't move because it is a tachymeter. It only moves when you start the stopwatch to show the average speed. :)
Delago 141 days, respond
How do I set city code for USA?

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