Casio G-Shock watches are sports-style, solar-powered wrist watches that keep time according to the radio-controlled atomic time signal broadcast by the UK National Physics Laboratory from a radio transmitter at Anthorn, Cumbria. Because the G-Shock is radio-controlled, the watch is basically self-setting. However, if you've been out of the UK and the watch is set to the wrong home city, the usually-accurate G-Shock will display the wrong time. Set the correct home city for your G-Shock to solve the problem. If the issue persists, you can also set the watch manually.
Set your home city
Press and hold the top left button on your Casio G-Shock until the watch beeps twice. Watch the stopwatch second hand; it will move to the currently-selected city code, indicating that you have accessed the watch's city code-setting mode.
Press the watch's bottom right button repeatedly to scroll through the available city codes. Choose "LDN" for London if you're in the UK.
Press the top left button on the watch to select the appropriate home city and return the watch to regular timekeeping mode. Note that the watch will automatically adjust itself to the correct current time based on the city you selected.
Set the time manually
Hold down the top left button for five seconds or until the watch beeps twice.
Press the top right button to turn the watch's automatic daylight savings time feature "Off" or "On."
Hold the bottom left button until the watch beeps again, indicating that you have entered its manual time-setting mode.
Use the top and bottom right buttons to adjust the hour and minute hands of your G-Shock to the desired time.
Press the bottom left button to save your changes. Press the top left button to return the watch to the regular timekeeping mode.
Force your Casio G-Shock to search for the radio-controlled time signal. Press and hold the watch's top left button for two seconds or until the watch beeps. Do not press any other button while the watch searches for and receives the signal; this can take up to 14 minutes.
Casio G-Shock setting instructions may vary by watch model. Contact Casio customer service for model-specific setting instructions for your G-Shock.