, what is the Relative Humidity?

To calculate relative humidity, you need two key measurements: the current air temperature and the dew point.

1. First, measure the current air temperature (T) using a standard thermometer. This should be in degrees Celsius or Fahrenheit.

2. Next, measure the dew point temperature (Td). This is the temperature at which the air would be fully saturated with moisture. You can use a dew point meter for this, or calculate it using a psychrometric chart if you know the wet bulb temperature.

3. Once you have these two measurements, you can calculate relative humidity (RH) using the following formula:

RH = 100% x (EXP((17.625Td)/(243.04+Td))/EXP((17.625T)/(243.04+T)))

This formula is based on the Magnus formula, which relates the saturation vapor pressure of water to temperature.

4. Plug your measurements into the formula to get the relative humidity. This will be a percentage, with 100% indicating fully saturated air (i.e., the dew point is equal to the current temperature) and 0% indicating completely dry air.

Remember, relative humidity is a measure of how much moisture the air is holding relative to the maximum amount it could hold at that temperature. So, it can change as the temperature or dew point changes, even if the actual amount of moisture in the air stays the same.