Refractometers and water heaters

I'm sure nobody on here is as dumb as I am, lol. But don't leave your refractometers for a prolonged time on top of your water heater. My water mixing station is in my mechanical room, along with my water heater. I was checking my salinity and when finished I left it sitting on top of the water heater. The next morning I walked in and tried to take another reading. Well, let's just say that the whole unit had warped/ melted! It's a BRS unit and im sure it would have done it to any brand, but I couldn't imagine it getting hot enough to do that...any way, I guess I'll order another from BRS, haha.