Why is it that hourmeters tend to fog?

[PSG-1]

I've seen this on more than one boat.


This is the hour meter that's currently on my jetboat. The hour meter I had before this, when the Tigershark engine was in the boat, was also constantly fogging up.

My parents have an 18 foot Sea Hunt with a 150 Merc, and the hour meter on that boat is fogged up.


Notice that my other gauges are not fogged, it's just the hour meter.



So, what gives? They seem to be able to make other gauges that don't fog up, what's the issue with hour meters?

 

[JMichael]

Purely speculation here but my guess would be that whatever electronics are inside the HR meter, they're producing more heat than other gauges and that's what's causing the moisture to vaporize and fog to form on the lens.