The Casio F-91W has an extensive reputation. Affordable, simple, linked to terrorism (no joke), and equipped with one of the worst backlights, it has managed to become one of the most popular watches on the planet. Cloned and counterfeited to exhaustion, the F-91W has been with us for more than three decades, but its "Water Resist" legend on the front makes us wonder: How resistant is it really? Benjamin Lowry from Watches of Espionage decided to look for the answer at almost five thousand meters deep...
Available information indicates that the Casio F-91W arrived on the market in June 1989, as a replacement for the (very similar) F-87W. Resin strap, stainless steel case and buttons, seven years of battery life, no smart features, and an unbeatable price (17 euros at the time of writing) place it almost always among the best-selling watches (in fact, it is number one on Amazon Spain). It is basic, it doesn't get in the way, and it does its job well, three aspects that many "smart" devices could adopt.
Now, what happens with that "Water Resist" on the front? An old copy of its official page on Casio UK indicates that on the F-91W-1XY model it equates to "50 Meters / 5 Bar", and that makes it suitable for swimming or immersion, but other sources talk about "30 meters / 3 Bar", and they barely support a little rain. Beyond the differences, Benjamin Lowry from Watches of Espionage decided to go in depth... literally.
Lowry got in contact with Josh Konicki (although technically it was the other way around), who specializes in deep-sea recovery operations, and frequently works for the US government. At the same time, Konicki is a watch enthusiast, and takes the opportunity to evaluate its resistance. The key to this experiment is the CURV 21, a remotely operated vehicle weighing 2.9 tons that can descend to 6,000 meters. Needless to say, the Casio F-91W would end up shattered at a fraction of that depth without help... and that's what it received.
A Casio Watch in the Depths
This is the "hydro-mod", the official name for filling the inside of the watch with mineral oil. The oil is virtually impossible to compress, and when the CURV reached 4,950 meters with a "hydro-modded" F-91W, the watch kept running without any issues.
To wrap up, I'll share a video published by the Defender channel in mid-2023, where we can see the hydro-mod process, and a similar test at 200 meters depth.
Official site: Click here
