During the application of a coating, the presence of moisture in the environment, or on the work surface, often results in a poor quality finish. Problems such as poor adhesion of the coating, delayed drying time or premature corrosion of the substrate can occur.

Before proceeding, it is essential that the air temperature and relative humidity (RH) are measured to calculate the dew point. The difference between this and the surface temperature is displayed as ∆T, with a warning if necessary.