View source for Casio F-91W

{{Short description|Digital watch produced since 1989}}
{{Use mdy dates|date=March 2025}}
{{Infobox watch
| name=Casio F-91W
| image=Casio F-91W 5051.jpg
| caption=Casio F-91W-1 watch with a resin case and resin [[watch strap|strap]]
| introduced= June 1989<ref name=news3lv>{{Cite web|url=http://news3lv.com/around-the-web/the-case-of-an-iconic-watch-how-wikipedia-and-writers-create-false-facts-from-thin-air|title=The case of an iconic watch: how lazy writers and Wikipedia create and spread fake 'facts'|last=Moyer|first=Phillip|date=June 15, 2019|website=[[KSNV]]|access-date=June 19, 2019}}</ref>
| type=[[Quartz clock|Quartz]]
| display=[[Watch#Digital|Digital]]
| manufacturer = [[Casio]]
}}
The '''Casio F-91W''' is a [[digital watch]] manufactured by Japanese electronics company [[Casio]]. Introduced in June 1989<ref name='news3lv' /> as a successor of the F-87W,<ref>Casio: General Catalog (1984): The Casio Collection. A Superb Selection of Modern Timepieces</ref> it is popular for its low price, long battery life and iconic design.<ref name="bbc">{{cite news|date=February 4, 2020|title=Casio F91W-1: The retro watch with a strange double life|url=https://www.montredo.com/en-gb/casio-f91w-1/|url-status=live|archive-url=https://archive.today/20250127201140/https://www.montredo.com/casio-f91w-1-the-retro-watch-with-a-strange-double-life/|archive-date=January 27, 2025|access-date=January 27, 2025|publisher=Montredo}}</ref> As of 2011, annual production of the watch is 3 million units, which makes it the most sold watch in the world.<ref name="icon">{{cite web|title=Casio F-91W – the classic quartz digital watch|url=https://www.iconeye.com/opinion/icon-of-the-month/casio-f-91w|website=ICON|date=August 19, 2011|publication-date=August 19, 2011|access-date=August 6, 2019|archive-date=July 29, 2019|archive-url=https://web.archive.org/web/20190729035310/https://www.iconeye.com/opinion/icon-of-the-month/item/9473-casio-f-91w|url-status=live}}</ref>

== Specifications ==

=== Design ===

Designed by Ryūsuke Moriai as his first design for Casio,<ref name="abtw">{{cite news|url=https://www.ablogtowatch.com/tokyo-man-designs-casio-g-shock-watches-ryusuke-moriai/|title=An Afternoon In Tokyo With The Man Who Designs Casio G-Shock Watches|publisher=[A Blog To Watch|date=April 16, 2017|access-date=July 6, 2019|author=Ariel Adams}}</ref> the case of the F-91W measures {{convert|37.5|by|34.5|by|8.5|mm}}. The case is primarily made of [[Synthetic resin|resin]],<ref>{{Cite web|title=F-91W-1 {{!}} Digital {{!}} Youth {{!}} Timepieces {{!}} CASIO|url=https://www.casio-intl.com/asia/en/wat/watch_detail/F-91W-1/|access-date=February 16, 2022|website=CASIO Official Website|language=en}}</ref> with a [[stainless steel]] caseback and buttons, with the manufacturer's module number, 593, stamped on the caseback. The resin strap is {{convert|18|mm}} at the fitting and 22&nbsp;mm across the widest part of the lugs. The total weight is {{convert|21|g}}.

=== Features ===
The F-91W has a [[chronograph]], featuring precision of {{frac|1|100}} seconds with a count up to 59:59.99 (nearly one hour). The chronograph is also able to mark net and split times (i.e. laps). Other features include an hourly time beep, a single daily alarm lasting 20 seconds and an annual calendar. The watch does not make allowances for [[leap year]]s as there is no provision to record the year. Due to this, the month of February is always counted as 28 days.<ref name="casiofeatures">{{cite web|url=http://www.casio.com/products/Timepiece/Classic/F91W-1|title=F91W-1 Classic Timepiece|publisher=Casio|access-date=April 27, 2011}}</ref> The watch uses a faint green [[Light-emitting diode|LED]] backlight located at the left of the display for illumination (in earlier units it was an amber microlight). According to the manufacturer estimates, the watch is reported to be accurate to ±30&nbsp;seconds per month.<ref name="casiofeatures" />

The [[Quartz clock|quartz]] [[Movement (clockwork)|movement]], designated ''Module 593'', is powered by a single [[CR2016]] 3-volt [[lithium]] button cell rated to a stated battery life of 7 years.<ref>{{cite web|title=F91W-1 {{!}} Steel Black Digital Watch {{!}} CASIO|url=https://www.casio.com/us/watches/casio/product.F-91W-1/|website=CASIO Official Website}}</ref>

=== Water resistance ===

The front of the watch is marked "[[Water Resistant mark|Water Resist]]".<ref name="casiofeatures" /> The black version (F91W-1)<ref name="casiofeatures2013uk">{{cite web|url=http://www.casio.co.uk/products/timepieces/casio-collection//Product/F-91W-1XY/|title=F-91W-1XY|publisher=Casio|access-date=May 22, 2013|archive-date=May 30, 2011|archive-url=https://web.archive.org/web/20110530022746/http://www.casio.co.uk/products/timepieces/casio-collection//Product/F-91W-1XY/|url-status=dead}}</ref> is "30&nbsp;meter / 3&nbsp;bar" (i.e. 100 feet / 44 psi), the ISO standard meaning of which is: "Suitable for everyday use. Splash/rain resistant. NOT suitable for showering, bathing, swimming, snorkeling, water related work and fishing".

== Operation ==

[[File:Casio F-91W 82T38575.jpg|thumb|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]]

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 clock|24-hour]] modes, depending on what mode the watch is currently in.<ref name="manual">{{cite news|url=http://support.casio.com/storage/en/manual/pdf/EN/009/qw593.pdf|title=Manual|publisher=Casio|access-date=November 26, 2014}}</ref>

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.

== Usage in terrorism ==
{{further|Seton Hall reports#Detainees' profile}}
[[File:Al Qaida watch timer on perf board 84071 -abc.jpg|thumb|This improvised timer for a time bomb was captured in the early 2000s.]]
The US government became suspicious of Afghans who wore Casio watches due to their ability to be used as timers for [[improvised explosive device]]s, a tactic favored by [[al-Qaeda]].<ref>{{cite news|title=Guantánamo Bay files: Casio wristwatch 'the sign of al-Qaida'|url=https://www.theguardian.com/world/2011/apr/25/guantanamo-files-casio-wristwatch-alqaida|newspaper=[[The Guardian]]|date=April 25, 2011|first=James|last=Ball}}</ref><ref>{{cite news|url=https://www.bbc.co.uk/news/magazine-13194733|title=Casio F-91W: The strangely ubiquitous watch|work=[[BBC News]]|date=April 26, 2011|first=Denise|last=Winterman}}</ref>

According to secret documents issued to interrogators at [[Guantanamo Bay detention camp|Guantanamo Bay]], obtained<ref>{{cite web|url=http://www.theguardian.com/world/interactive/2011/apr/25/guantanamo-files-interrogators-al-qaida-taliban|title=Guantánamo files: How interrogators were told to spot al-Qaida and Taliban members|date=April 25, 2011|website=The Guardian|access-date=April 10, 2019|author=<!--not given: it's a document leak-->}}</ref> and released by ''[[The Guardian]]'', "the Casio F-91W digital watch was declared to be 'the sign of [[al-Qaeda]]' and a contributing factor to continued detention of prisoners by the analysts stationed at Guantanamo Bay. Briefing documents used to train staff in assessing the threat level of new detainees advise that possession of the F-91W and the A159W, available online for as little as £4, suggests the wearer has been trained in bomb making by al-Qaeda in Afghanistan."<ref name="guardian_ball">{{cite news|first=James|last=Ball|date=April 25, 2011|url=https://www.theguardian.com/world/2011/apr/25/guantanamo-files-casio-wristwatch-alqaida|title=Guantánamo Bay files: Casio wristwatch 'the sign of al-Qaida'|work=[[The Guardian]]|location=London|author-link=James Ball (journalist)}}</ref> United States [[military intelligence]] officials have identified the F-91W as a watch that terrorists use in constructing [[time bomb]]s.<ref name="MilitaryCommissionCharges2005NovJabranAlQahtani">{{cite web|url=http://www.defenselink.mil/news/Nov2005/d20051104qahtani.pdf|title=USA v. al Qahtani|date=November 7, 2005|access-date=February 27, 2007|publisher=[[US Department of Defense]]}}</ref><ref name="eledah">{{cite news|title=Combatant status review board for Mohammed Ahmad Said el Edah|date=October 6, 2004|url=https://www.nytimes.com/interactive/projects/guantanamo/detainees/33-Mohammed-ahmad-said-al-edah/documents/5|work=[[The New York Times]]}}</ref><ref name="MotherJones060712">{{cite web |last=Gilson |first=Dave |date=July 12, 2006 |title=Why Am I in Cuba? |url=http://motherjones.com/news/feature/2006/07/detainee_sidebar.html |work=[[Mother Jones (magazine)|Mother Jones]]}}</ref><ref name="SummaryOfEvidence415">{{cite web|url=http://www.dod.mil/pubs/foi/detainees/csrt_mar05.pdf#216|title=Summary of Evidence for <!--Sabri Mohammed Ebrahim Al Qurashi's – name not present in the document--> Combatant Status Review Tribunal|page=216|date=October 13, 2004|url-status=dead|archive-url=https://web.archive.org/web/20060731081044/http://www.dod.mil/pubs/foi/detainees/csrt_mar05.pdf#216|archive-date=July 31, 2006|df=mdy-all}}</ref>

This association was highlighted in the [[Denbeaux study]], and may have been used in some cases at Guantanamo Bay.<ref name="nationaljournal">{{cite web|url=http://nationaljournal.com/about/njweekly/stories/2006/0203nj4.htm|title=Empty Evidence|date=February 3, 2006|work=[[National Journal]]|url-status=dead|archive-url=https://web.archive.org/web/20080704000658/http://nationaljournal.com/about/njweekly/stories/2006/0203nj4.htm|archive-date=July 4, 2008}}</ref> An article published in ''[[The Washington Post]]'' in 1996 reported that [[Abdul Hakim Murad (militant)|Abdul Hakim Murad]], [[Wali Khan Amin Shah]], and [[Ramzi Ahmed Yousef]] had developed techniques to use commonly available Casio digital watches to detonate time bombs.<ref name=WashingtonPost19960721>{{cite news|url=https://www.washingtonpost.com/wp-srv/national/longterm/twa800/bomb.htm|title=New Devices May Foil Airline Security|page=A01|newspaper=[[The Washington Post]]|first=R. Jeffrey|last=Smith|date=July 21, 1996|access-date=March 14, 2008|author-link=R. Jeffrey Smith}}</ref> Casio watches were mentioned almost 150 times in prisoner assessments from Guantanamo.<ref>{{cite web|author=Batya|date=July 9, 2020|title=How did the Casio F91W Become a Terrorist Icon?|url=https://reaperfeed.com/how-did-the-casio-f91w-become-a-terrorist-icon/|url-status=live|archive-url=https://archive.today/20200728060545/https://reaperfeed.com/how-did-the-casio-f91w-become-a-terrorist-icon/|archive-date=July 28, 2020|access-date=January 27, 2025|website=Reaper Feed}}</ref>

On July 12, 2006, the magazine ''[[Mother Jones (magazine)|Mother Jones]]'' provided excerpts from the transcripts of a selection of the Guantanamo detainees.<ref name="MotherJones060712"/> The article informed readers:

{{quote|More than a dozen detainees were cited for owning cheap digital watches, particularly "the infamous Casio watch of the type used by Al Qaeda members for bomb detonators".}}

The article quoted Guantanamo Bay detainee [[Abdullah Kamel Abdullah Kamel Al Kandari]]:

{{quote|When they told me that Casios were used by Al Qaeda and the watch was for explosives, I was shocked&nbsp;... If I had known that, I would have thrown it away. I'm not stupid. We have four chaplains [at Guantanamo]; all of them wear this watch.}}
== Variants ==

{| class="wikitable"
|+
!Model name
!Description
|-
|F-91W-3, F-91WG-9
|Similar to the original F-91W, but including a green and gold trim respectively on the face.<ref>{{Cite web|title=F-91WG-9 {{!}} VINTAGE SERIES {{!}} Timepieces {{!}} CASIO|url=https://www.casio-intl.com/np/en/wat/watch_detail/F-91WG-9/|url-status=dead|archive-url=https://web.archive.org/web/20200804024433/https://www.casio-intl.com/np/en/wat/watch_detail/F-91WG-9/|archive-date=August 4, 2020|access-date=|website=CASIO Official Website|language=en}}</ref>
|-
| F-91-WB series
| Simplified case print, print on face and strap: blue-gray on black, bronze on black, white on blue, gray on white. <ref>{{Cite web|title=Casio Product F-91WB-1|url=https://www.casio.com/intl/watches/casio/product.F-91WB-1A/|url-status=live|archive-url=https://archive.today/20250127203847/https://www.casio.com/intl/watches/casio/product.F-91WB-1A/|archive-date=January 27, 2025|access-date=January 27, 2025|website=www.casio.com|language=en}}</ref>
|-
| F-91-WC series
| Neon colors for case, face and strap: orange, blue, green, pink, beige and yellow.<ref>{{Cite web|url=https://www.casio.co.uk/products/timepieces/casio-collection/|title=Casio Collection {{!}} Timepieces {{!}} Products {{!}} CASIO|website=www.casio.co.uk|language=en|access-date=June 8, 2019|archive-date=May 30, 2011|archive-url=https://web.archive.org/web/20110530022742/https://www.casio.co.uk/products/timepieces/casio-collection/|url-status=dead}}</ref>
|-
| F-91-WM series
| Metallic colored cases with black straps: grey, army green, blue, silver and gold.
|-
| F-91-WS series
| Translucent straps with muted case colors: blue, pink, white, and grey<ref>{{Cite web|title=Casio International {{!}} Timepieces {{!}} Digital {{!}} F-91WS-2 {{!}} CASIO|url=https://www.casio-intl.com/Asia/en/wat/watch_detail/F-91WS-2/|url-status=live|archive-url=https://archive.today/20250127203459/https://www.casio.com/intl/watches/casio/product.F-91WS-2/|archive-date=January 27, 2025|access-date=January 27, 2025|website=www.casio-intl.com|language=en}}</ref>
|-
| F-84W
| Japanese Domestic Market (JDM) model.  Uses the same 593 module, but the case design is more similar to the older F-28W and F-87W. It has lugs instead of an embedded strap.
|-
| F-94W
| Circular icon arrangement in the display.
|-
| W-59
| Black case with rounded corners and blue accents on the face. Waterproof up to 50 meters.
|-
| A158W, A159W, A163W, A164W
| Chrome plated case, stainless steel band.
|-
| A159WGEA-1
| Ion plated gold stainless steel band, gold colored chrome plated case.
|-
| F-105W, A168W, A168WG, A168WEGM, A168WEM, W-86
| Equipped with [[Electroluminescence|electroluminescent]] backlighting instead of the LED backlight in the other variants. Available in black color with a resin strap or in silver or gold colors with a stainless steel bracelet. Slightly different icon arrangement on the display and a thicker case due to the backlight system. Some versions also feature a negative display.
|-
| LA680
| A smaller variant, marketed towards women
|}

== Counterfeits ==
[[File:Casio F-91 Module 593 Displaying CASIo.jpg|thumb|Holding the right button for 3 seconds in the main timekeeping mode leads the display to show "CASIo", which is useful to spot a counterfeit model (applicable for newer models of the F-91W and its variants, including F-94W and A158W)|alt=]]

[[Counterfeit watch|Counterfeits]] of this watch are very common, despite its low price tag. These counterfeits generally have a lower plastic build quality, narrower LCD viewing angles, louder and higher-pitched beeps, and significantly less accurate timekeeping than genuine models.<ref name="fakes">{{cite web|date=July 2018|title=Comparing a genuine Casio F91-W with a fake|url=https://www.burningimage.net/genuine-and-fake-casio-f91w/|url-status=live|archive-url=https://archive.today/20250127203119/https://www.burningimage.net/genuine-and-fake-casio-f91w/|archive-date=January 27, 2025|access-date=January 27, 2025}}</ref> The newer modules with the green LED light can be tested by holding the right button for over 3 seconds in the main timekeeping mode; this will lead the display to show "CASIo", as a test for authenticity. With the advancement in technology, however, some counterfeit models have also been developed to show this sign. A different way of assessing authenticity is to press all three buttons simultaneously, which has the watch enter a test mode. In that mode, an extra dot is seen with fake modules in some cases. <ref>https://www.burningimage.net/genuine-and-fake-casio-f91w/</ref> If the dot is not there, another indicator is if the dot that serves as a serif at the bottom of the leftmost day letter is a distance from the letter. A real F91W will have the serif nearly touching the letter. <ref>https://www.reddit.com/r/casio/comments/1i4fdfy/is_my_f91w_legitimate/</ref>

{{clr}}

== References ==
{{Reflist}}

== External links ==
* {{commons category-inline|Casio F-91W}}
* [https://www.casio.com/products/watches/classic/f91w-1 F91W-1 product page], Casio website

{{Casio}}

{{DEFAULTSORT:Casio F91w}}
[[Category:Casio watches|F91W]]
[[Category:Products introduced in 1989]]