Casio F-91W cheat sheet

Knowing the buttons

The F-91W has 3 buttons. Two on the left, one on the right.

The BOTTOM LEFT is button C.
The TOP LEFT is button L.
The BOTTOM RIGHT is button A.

Why these letters? Because that's what Casio themselves uses in the manual for this watch that nobody ever reads:

Knowing the screens

The F-91W only has 3 screens. Main timekeeping, alarm and stopwatch.

In main timekeeping, you see the clock and date. In alarm, AL is at the top. In stopwatch, ST is at the top.

Switching from 12-hour to 24-hour a.k.a. military time

From the main timekeeping screen, press A once. At the top left of the display a small 24H will appear. When it does, you are in 24-hour mode. Press A again to return to 12-hour time.

Note: In 12-hour time, the F-91W will display a small PM at top left for afternoon hours. If you are in 12-hour time and do not see PM at the top left, the clock is displaying morning hours.

Setting the time

From the main timekeeping screen, press C C C. When you do this, the seconds should be blinking. If the seconds are not blinking, press C until you get back to the main timekeeping screen, then press C C C again so the seconds start blinking.

Whatever is blinking is what you are setting

Anything that is blinking while doing this is the thing you are setting at that moment. Right now we're setting the seconds.

Note that if the F-91W has something blinking and you do not press any buttons for about 30 to 45 seconds, the watch will automatically cancel out of that setting and return you to the main timekeeping screen.

Setting the seconds

While the seconds are blinking, pressing A will reset the seconds to zero.

If the seconds are between 0 through 29, only the seconds are reset to zero when you press A.

If the seconds are between 30 to 59, the seconds are reset to zero and the minute advances by one when you press A.

Setting the hour

After the seconds are set, press L once. The hour starts blinking.

Use A to set the hour. If you press A once, the hour advances by one. If you press and hold A, the hour will scroll quickly until you let go of A.

Note: If you are displaying 12-hour time, you will see a PM at top left for afternoon hours. If the PM is not present in 12-hour time, morning hours are being displayed. If 24-hour time is being displayed, a small 24H at the top left of the display will be present no matter what hour is showing.

Setting the minutes

After the hour is set, press L once. The minutes start blinking.

Use A to set the minutes. Press once to advance one minute, or press and hold to scroll quickly to the minute you want to set to.

Published 2019 Nov 21