April 2025, Japan. Casio files an application with the Japan Patent Office. The mark it wants to protect is not a logo or a slogan. It is a model number: F-91W.
The office's first answer was no, according to Impress Watch. A model number, it said, is only a string of characters. Casio then sent evidence of how widely known the watch is, and the application was approved.
The Casio F-91W is a resin digital watch that Casio released in June 1989 as the successor to the F-87W. It has barely changed since. That raises one question: why would a company leave a product alone for more than three decades?
- Maker: Casio, Japan
- Released: June 1989, successor to the F-87W
- Movement: module 593, quartz, accurate to within 30 seconds a month according to Casio
- Size: 38.2 x 35.2 x 8.5 mm (1.5 x 1.4 x 0.3 in), 21 g, resin case, glass and band
- What made it different: a watch designed to be made as cheaply as possible without lowering quality
Where the F-91W came from
Casio's own heritage pages place the watch in a longer line. In 1974 the company launched the Casiotron, which it calls the world's first digital watch with an automatic calendar. The calendar knew which months were short.
The next step was the case. According to Casio, the F-100 of 1978 introduced a rigid resin case, an idea that later fed into the G-SHOCK.
In 1983 Casio released the first G-SHOCK, the DW-5000C, after about two years of development and more than 200 prototypes. That watch was built to survive shocks. The F-91W had a different aim: low cost.
By then Casio was already making watches in volume. Its heritage page says the company passed 100 million watches shipped in 1984, nine years and nine months after the Casiotron appeared in November 1974.
The following year brought the FS-10, a slim digital watch with the case and band made as one piece. According to Casio, it sold more than one million.
Casio's 1980s page lists the F-91W under 1989. It calls the watch a record-breaking bestseller with a strong, slim and lightweight resin case. The page gives no sales figure.
What the Casio F-91W does
The list of functions is short. According to Casio's product page, the F-91W has a daily alarm, an hourly time signal, an automatic calendar and an LED light. Its stopwatch measures to one hundredth of a second, up to 59 minutes and 59.99 seconds.
The battery is a CR2016 cell. Casio rates it at about seven years. The case, the glass and the band are all resin, and the watch weighs 21 grams. Impress Watch describes the water resistance as suited to daily life.
The face in the first photograph shows the layout. Casio prints the name and model number at the top, the words Alarm Chronograph in yellow, and a red WR mark between the words Water and Resist. A blue ring runs around the display. The screen shows the day, the date, the hour, the minutes and the seconds at once.
Few watches have a face this plain. The dial prints every function in capital letters: light, mode, alarm on-off, water resist. Wristwatch Tearoom praises this as information design: the face explains the watch.
Cheap on purpose, not careless
The F-91W was built to cost very little. Kinugasa Yutaka works in Casio's product planning department. He told Impress Watch in 2025 that the team used every idea it had to make the watch cheap. Quality, he said, was not allowed to drop.
One of those ideas is small. Most watches hold the strap with spring bars, which are pins that compress at both ends. According to Impress Watch, the F-91W uses press-fit pins that go in from one side. The saving was a few yen per watch.
Impress Watch also names the markets the watch was aimed at: the Middle East, India, Pakistan, Bangladesh, Africa and Southeast Asia. The original blue-ringed model, the F-91W-1, is still the best seller, even in the Middle East.
The word that appears when you hold a button
Hold the lower right button for about three seconds and the display spells CASIO. Impress Watch describes this as an authenticity check. It also reports that the feature was copied almost as soon as it appeared.
Counterfeits of the watch still circulate, and Casio still receives questions about them. That is where the trademark story and the question of change meet.
Kinugasa gave Impress Watch the reasoning. The original is so well known that changing it would make the result look like a fake. So Casio cannot change it carelessly, and sees no need to.
The sameness is the point. A watch that never changes is easy to recognize, and a copy has to match something fixed. Casio does not publish how many F-91W watches it has made. Kinugasa calls the total a very large number. Estimates of about three million a year circulate in print, but none comes from Casio.
What a museum kept
The Science Museum Group in London holds an F-91W in its collection, object number 2000-75. The record dates it to 1999 and says it was made in Japan. It is a black resin watch with alarm and stopwatch, still in its packaging, and the record lists a seven-year battery life. The museum lists the watch for its Making the Modern World gallery, and asks visitors to confirm in advance that it is on display.
The design critic Stephen Bayley, a co-founder of London's Design Museum, called the F-91W a "modest masterpiece", according to Gear Patrol. Its story differs from that of the Speedmaster NASA tested. This one answers a different question: how cheaply a good watch can be made.
Fans also repeat a story that an F-91W lost for more than twenty years was found buried in the ground and was still running. Impress Watch mentions it as a report that is well known among fans. It is not documented, so treat it as a story and not a fact.
How a budget watch became a fashion item
Fashion came later. According to Impress Watch, fans coined the term "Cheap Casio" for inexpensive models like it. Casio's own lines in Japan are called Casio Collection and Casio Classic.
Impress Watch dates the overseas boom to the late 2000s. It started in Europe, among young people who wore the A168 digital watch as a retro accessory, and then spread to the United States.
Kinugasa told the magazine that Casio designs these models to sell for at least five years, and ideally ten. Impress Watch counted thirty-six years on sale for the F-91W in 2025.
A new color, the same watch
Casio does still release colorways. On August 22, 2025, it put a green version, the F-91W-3JH, on sale in Japan. Impress Watch reports that it follows the standard black design, with green accents in place of blue.
Impress Watch ties the green to its symbolic meaning in Arab and Islamic contexts.
Back to April 2025. The Japan Patent Office had first seen a string of characters. After reading Casio's evidence, it saw a name. A watch that has kept its specification since 1989 had become a brand.
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Sources
- Casio, F-91W-1 product page (specifications): casio.com
- Casio, Heritage 1970s (Casiotron, F-100): casio.com
- Casio, Heritage 1980s (G-SHOCK, F-91W entry): casio.com
- Impress Watch, "The world rediscovers Cheap Casio" (October 9, 2025; interview with Casio's Kinugasa Yutaka): watch.impress.co.jp
- Impress Watch, F-91W-3JH announcement (August 20, 2025): watch.impress.co.jp
- Science Museum Group, Casio gents LCD digital watch, object 2000-75: collection.sciencemuseumgroup.org.uk
- Wristwatch Tearoom, the story of the F-91W (June 1989 release, F-87W predecessor): wristwatch-tearoom.com
- CasioRestore, F-91W technical data and model information: casiorestore.com
- Gear Patrol, Casio F-91W review (Stephen Bayley quotation): gearpatrol.com
- Photographs by Multicherry, Wikimedia Commons, CC BY-SA 4.0: front view, LED light, CASIO display, left side, license
Sources compiled and text drafted with AI assistance. Published by Unseend.