Seeing the thread about the oil filled omega reminded me to finally post this...
I did this a couple of years ago with a bright green Casio F-91W with Extra Virgin Olive Oil, because why the hell not :D
I work offshore occasionally and in the past couple of years I have had the opportunity to conduct some "testing".
On one particular trip I stuck it in a Triaxial cell, filled it with water and then pressurised it to about 1000kPa (100m water depth) and she pulled through perfectly (photos on my old phone unfortunately).
I took the watch back home and forgot about it until summer last year when I was involved in some deep water work...
Here she is, notice the bubble, harder than you'd think to attach the back of a watch with the tiny screws when submerged in a bowl of Extra Virgin :p
So I strapped it to our sea bed template.
The first test was 531.4m water depth for 4 days.
Back to the surface and SUCCESS!
A quick clean up
After an inspection I noticed some fine cracks to the LCD display, not the plastic "crystal" but the actual screen of the LCD.
Later that day I noted that the bubble of air inside was bigger than before, which is understandable considering this is sold as a water resistant watch and offers no promise of water proof depth rating.
With the 531.4m under its belt, I decided it best to test it to the deepest water depth I could, 984.5m!
Again, I zip tied it to the sea bed template and down she went...
3 days later she came back up with the frame annnnnnnnnnd...
IT LIVES!
I was overjoyed, this £10 watch that I filled with Extra Virgin Olive Oil had surpassed the ratings of a lot of expensive purpose made dive watches! It has now earned a special place in my collection as the little watch that could.
A special mention should be given to those brave olives that gave their lives for this horological achievement.