Casio F-91W cheat sheet
If you're going to rock an F-91W, this is a quick guide on how to set the time, set the date and a few other tips and tricks.
Recently, I bought another watch, an F-91W in a monochrome gray color scheme, the F-91WM-1B. The standard model has the black with blue border, but I liked the gray one because the only colors seen are black, white and grays.
I figured I might as well write up a guide on this, because as simple as the watch is, amazingly some get confused by it. After reading this, you won't be confused anymore and will be able to operate the F-91W with ease.
This guide applies to all F-91W models regardless of color, and will also work on the F-84W, F105W and W59. It will also work on a few other models that I will list in a moment.
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.
Setting the date
The F-91W does have a date feature.
Why set the date?
The reason to set the date is so that the day is correct. For example, June has 30 days and July has 31. If you have the date set incorrectly, at some point the watch will show the incorrect day of the month at the top right of the display.
The F-91W does not accommodate for leap years. A leap year happens every 4 years where instead of February having only 28 days there is 29. During a leap year, you will have to reset the date on March 1 so it is correct again. This is not a big deal since you only have to do this once every 4 years.
(Tip: If you need a watch where you don't have to worry about leap years, upgrade to a Casio AE1200 or WS1600H.)
Setting the month
After the minutes are set, press L once. The screen changes where the clock disappears and only the month shows, which will be blinking.
Use A to set the month.
If you forget which number is which month, use the list below.
1 = January
2 = February
3 = March
4 = April
5 = May
6 = June
7 = July
8 = August
9 = September
10 = October
11 = November
12 = December
Setting the day
After the month is set, press L once. The day at top right of the display will be blinking. Use A to set the day.
Setting the weekday
After the day is set, press L once. The weekday at top middle of the display will be blinking.
Use A to set the weekday.
The weekday is displayed using two letters on the F-91W display. This is what each means:
SU = Sunday
MO = Monday
TU = Tuesday
WE = Wednesday
TH = Thursday
FR = Friday
SA = Saturday
Exiting the settings
Press C once.
Setting the alarm
Press C from the main timekeeping screen, and AL will appear at the top middle of the display to indicate you are on the alarm screen.
Turning the alarm on or off, and turning hourly signal on or off
From the alarm screen, press A. Depending on how the alarm/signal is set, one of four will be displayed:
Nothing at top left: Alarm is OFF, hourly signal is OFF.
Audio wave icon at top left: Alarm is ON, hourly signal is OFF.
Bell icon at top left: Alarm is OFF, hourly signal is ON.
Audio wave icon and bell icon at top left: Alarm is ON, hourly signal is ON.
You can go through each one of these by repeatedly pressing A.
Note: When the alarm is ON, the watch will sound a beep for 20 seconds at alarm time you have set. When the hourly signal is ON, this is not an alarm. The hourly signal is a double beep you will hear at the top of every hour.
Testing the alarm tone
From the alarm screen, press and hold A. In about 2 seconds, you will hear the alarm tone test. Let go of A to stop the test.
Setting the alarm time
From the alarm screen, press L.
The alarm hour will blink. Press A to adjust the alarm hour.
Press L again. The alarm minutes will blink. Press A to adjust the minutes.
Press L again to stop all blinking. The alarm time is now set.
Note: In 12-hour time, afternoon hours are indicated by a PM at the top left of the display. If no PM is present, a morning hour is set.
Using the stopwatch
Press C repeatedly until ST appears at the top middle of the display.
Press A to start the stopwatch. Press A again to stop the stopwatch.
Press L to reset the stopwatch to 00:00.00
Using the lap feature
This feature is to measure lap times and/or use for recording first and second runner finishes.
Press A to start the stopwatch. Press L. LAP will appear on the display. The stopwatch freezes the recorded time but is still running in the background. Press L again to go back to the stopwatch. From this point you can press A to stop and then L to reset to zero.
Measuring first and second runner finishes is as follows: Press A to start the stopwatch. When you want to record the first runner's time, press L. When you want to record the second runner's time, press A. After that, what is on the display is the first runner's time. Press L to see the second runner's time. Then press L again to reset to zero.
F-91W Tips and tricks
These are a few things I do to extend the use of the F-91W.
Seeing the full date quickly
From the main timekeeping screen, press in this order: C C C L L L. You can remember this easily as "down down down, up up up" buttons on the left side of the watch.
Doing this will show a blinking month and the day at top right.
When done reading the date, press C once to exit.
Technically, what you're doing here is going to the month setting, but it's a fast way just to see the full date when you need to.
Using the alarm as a timer
The F-91W does not have a countdown timer but does have an alarm. While you can't see the countdown using an alarm in this way, you can hear the beep, and sometimes that's all you need.
If you always start your "timer" at the top of an hour, quarter-hour or half-hour mark, this makes things easier.
Example 1: If at 2:30pm I want to set an alarm to sound 90 minutes later, that's 1 hour and 30 minutes. One hour after 2:30pm is 3:30pm, and 30 minutes after that is 4:00pm.
Example 2: If at 2:30pm I want to set an alarm to sound 45 minutes later, that's 1 half-hour and 1 quarter-hour. 2:30pm + 30 minutes is 3:00pm, and 15 minutes from 3:00pm is 3:15pm.
"Isn't the stopwatch technically a timer?"
No. The stopwatch counts up and not down. You can use the stopwatch as a "count-up" timer, but there is no way for the F-91W to beep when the stopwatch reaches a certain elapsed time. When you use the alarm as a timer of sorts, you get the beep.
A microfiber towel cleans the watch face easily even when dry
The watch face on the F-91W is either acrylic or a material similar to it. To clean the watch face without scratching, just use a microfiber towel. It actually works better than a paper towel.
Never use tissue paper to clean the watch face, as that is abrasive.
For the back of the watch and the strap, lightly dampen the towel so those areas get cleaned well. But for the face, you can use the towel dry and it will work nicely.
Are there any Casio watches that will automatically set the time and date for me?
Yes. Any Waveceptor model will automatically set the time, which is especially useful for Daylight Savings Time changes.
Other Casio watches that these instructions will work for
The instructions here will also work for these models:
Published 2019 Nov 21