Here you go Hanzo, you can read all about it.starting at the bottom of page 1. https://support.casio.com/storage/en/manual/pdf/EN/009/qw2632.pdf
As a prepper, I have thought about how we would tell time after the SHTF! ALL of the electric and battery powered clocks and watches will be dead. The surviving smartphones and computers will be too valuable to carry around as time pieces. Mechanical, solar and movement powered watches will be invaluable, as will wind-up clocks!
If things are at that stage, no need time keeping per se. The sky will tell you how much light you have.