I've only had extensive experience with two cyclocomputers. One was the CatEye ATC CC-8000 which was actually sealed and waterproof. The other is my current FlightDecks. I've used others though but not enough in the rain. Both of the previously mentioned computers operated fine in the rain. However, one had sealed buttons and the other had no buttons on the computer itself for on-bike operations and the FlightDeck hood buttons seemed relatively sealed. One suggestion is to smear a little bit of vasoline around the contacts to keep the water from shorting them out or corroding them.