Hiding inside the box are thermometers for measuring air temperature and hygrometers to measure humidity.

Capacitors with an exposed and porous dielectric can be used to measure humidity in air.

Modern electronic devices use temperature of condensation (the dew point), or changes in electrical capacitance or resistance to measure humidity differences.

Equipped to measure humidity, rainfall and temperature, they will help make accurate forecasts, specifying the rainfall variability.

When measuring humidity, professionals use a hair hydrograph — a horse's hair suspended between two points that reacts to changing humidity — but they are expensive.