Thank you for your email regarding your Aprilaire humidistat. If you turn the dial from left to right you should hear two clicks. The actual humidity in your home will be the area between the two clicks. For example, if the humidistat clicks at 30% and 36% your actual humidity would be 33%. There is not a way to calibrate the humidistat. It is unclear from your email if the original humidistat is an Aprilaire humidistat, so it is difficult to say if it is out of spec. The accuracy of our Aprilaire manual humidistats are +/- 5%
The moisture on your windows is due to the surface temperature of your windows reaching dew point. This occurs when there is more humidity in the home than what the home can hold based on the current outdoor temperature. As the temperature outside drops you want less humidity in your home. For example when the outdoor temperature is 20F or above we recommend 35% humidity at a room temperature of 70F. If the outdoor temperature drops to 0F you'll want 25%.
Thank you for giving us the opportunity to be of service