page_title: Casio F-91W
section_title: Operation
hierarchical_section_title: Casio F-91W / Operation
caption_attribution_description: English: A Casio F-91W digital watch, circa 2013.
context_page_description: The Casio F-91W is a digital watch manufactured by Japanese electronics company Casio. Introduced in June 1989 as a smaller counterpart to the 1983 DW-5000, it is popular for its reliability, long battery life, and low price tag. Annual production of the watch is 3 million units per year.
context_section_description: The watch is controlled by three side-mounted push-buttons. 
  The upper left button, labeled "Light", turns on the light, cancels the alarm, resets the stopwatch or marks the split (lap) time, and is used for selecting settings.
  The lower left button, labeled "Mode", cycles the modes of the watch: time display, alarm, stopwatch, and time/date adjustment.
  The right button, labeled "Alarm On-Off/24hr", is the function button: when used, it starts and stops the stopwatch, changes the settings currently being adjusted, or switches between the 12- and 24-hour modes, depending on what mode the watch is currently in. Pressing all three buttons at the same time will fill all the cells on the LCD until any button is pressed again.
  The time or date is adjusted by pressing the lower left button three times to bring the watch to time adjustment mode. The top left button is used to cycle through seconds, hours, minutes, month, date, day, and normal mode. The right button is used to adjust the flashing value displayed. Unlike any other value, the seconds can only be zeroed. Should this happen before 30 seconds, the watch will zero in at the beginning of the current minute. After 30 seconds it will start the next minute as displayed. When the adjustments are finished, the bottom left button can be pressed once to return the watch to normal mode.
  The watch display shows the day of the week, day of the month, hour, minute, seconds, and the signs PM in the afternoon – or 24H (24-hour clock) – at all times, the alarm signal status (bar of vertical lines), and the hourly signal status (double beep on the hour, shown as a bell) are present when activated in the alarm mode.
  In stopwatch mode, minutes, seconds, and hundredths of a second are shown.
caption: Casio F-91W, in regular timekeeping mode and using the 24-hour display option. The watch is currently set to sound the alarm and hourly chime
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