Sometimes gauges are installed in humid environments, and it is important that the correct instruments are selected for these conditions.
To prevent condensation entering and obscuring the dial face of a gauge, a gauge filling should be used. The liquid filling (usually glycerine) will create a seal, thus preventing moisture from entering the dial casing. If moisture does enter the gauge, condensation can form inside of the window and obscure visibility. The water moisture can also freeze in sub-zero ambient temperatures, and the resultant expansion in mass can damage the internal mechanism.
A waterproof and corrosion resistant case should also be considered, such as stainless steel or phenolic.
Ingress protection (IP) 67 as a minimum should be in place for the instrument.
For extreme humidity/wet conditions, further protection should be put in place, including stainless steel internal parts and corrosion-resistant stainless-steel laser welded case construction.