The program ONLINE_PRIESTLEY_TAYLOR calculates potential evapotranspiration (PET) by the Priestley-Taylor method.

1. The input is:   (a) the chosen month, (b) air temperature T_a (^oC), and (c) net radiation Q_n (cal cm^-2 d^-1).

2. The output is:   (a) daily PET (cm d^-1), and (b) monthly PET (cm).

3. Potential evapotranspiration (PET) is a function of:   (a) net radiation Q_n, (b) Penman's ratio α, (c) mass density of water ρ, and (d) heat of vaporization λ.

4. Input allowable ranges: (a) air temperature, 0-40 ^oC; (b) net radiation, 100-1000 cal cm² d^-1. Input data outside of these ranges will trigger error messages and stop execution.