The calculator allows you to experiment with the relationships between the variables in the Poisson's equation.
Sample values are supplied to give you a feeling for what a "normal" value might be for the initial pressure and temperature. You can click on "CALCULATE" to compute the potential temperature for an air parcel with the default values. Or, by changing the value of inital pressure and initial temperature calculate potential temperature.
NOTE: Originally, the initial temperature should be converted to degrees Kelvin. Here, this conversion is made for you.