Why is it important to measure humidity?
It is important to measure humidity because maintaining the correct temperature and humidity helps to keep products from spoiling. Products can spoil for a number of reasons, including:
Condensation
Bacteria and germ growth
Mold
Electrostatic discharge
Corrosion
Warping
To prevent these problems, industries with products at risk of spoilage install instruments to measure humidity and temperature continuously through the manufacturing process and also while products are stored.
What types of instruments measure humidity?

A psychrometer (wet/dry bulb) sensor measures humidity through the cooling effect of evaporation
Instruments that measure humidity include but are not limited to:
Why calibrate humidity?
It is important to calibrate humidity instruments regularly, to make sure they are performing within their manufacturers' specifications. Calibration lets you know that measurements made with these instruments are accurate so that quality can be maintained.