The Casio F-91W was once the watch of choice for IT professionals with kids at home and the occasional Al Qaida terrorists, but recently it has become a piece of ’90s nostalgia ripe for watch enthusiast tinkering.

Modded Seiko Watch
Modded Seiko Watch

Usually, when I think watchmodding, I think Seiko. Modding Seiko divers is so popular there are countless internet shops and communities just to support the endeavor. But modding an old Casio is something different indeed.

YouTuber N-O-D-E, the video above, took an old Casio F-91W watch and added a few modern features. He removed the iconic face design and replaced it with a simple letterbox. He replaced the classic green LED with a brighter white light. And he even stuck a ntag213 NFC chip in the watch case for communication between the watch and a tablet. He also stuck an SD card slot on the back.

He’s not the only one tinkering with these things; Watchuseek forums user hansp inverted the colors on the screen on a F-91W with linear polarizing film and the result is pretty awesome. Others have improved the LED light – in the original the bulb shines at a 90-degree angle away from the face of the watch.

I think my favorite, however, is the hydro mod, which involves injecting oil into the watch case. According to The Watch Site forums user Homocaballus, the oil keeps water out of the watch if it is submerged. Some even go so far as to use Olive oil because it gives the face a greenish tint. YouTuber Artur Martins hydro-modded his F-91W and says it has survived snorkeling trips and swimming pools for the last three years.