Remember that a prerequisite of determining the dew points of all of these methods is the positive effect of air temperature, expressed in degrees Celsius.
If you have a psychrometric table, and in terms of the problem specified temperature and humidity, initially set the temperature to Celsius. Then find the corresponding parameters, respectively, in the top horizontal row and left vertical column of this table. At their intersection will be the dew point temperature, expressed also in degrees Celsius. If necessary, move the result to the Kelvin.
Also find the dew point can be found mathematically. To do this, first bring the temperature specified in the conditions of the problem, in degrees Celsius. Then find the auxiliary parameter γ according to the following formula: γ=(17,27 T/(237,7+T))+ln(RH) where T is temperature °C, RH - relative humidity, %.
Now substitute the auxiliary parameter γ in the second formula should appear as follows: Tp=237,7 γ/17,27-γ), where Tp is the dew point temperature, γ is a value determined in the previous calculations.
In the presence of psychrometrics hygrometer (not an hygrometer of a different type) to determine the dew point can be directly. To do this, first make sure that the preparation work was made long ago, and he came into work mode. Then read the readings of the wet-bulb thermometer - they will be equal to the dew point. If you want to find only the magnitude, but not the humidity, it does not require even the use is located on the body of the instrument psychrometric table.
The result of the computation or to the direct determination of the dew point move to the unit where it needs to be expressed according to the conditions of the problem. It could be the Kelvin and Celsius, Fahrenheit, etc.