Wet-surface evaporation equations related to the Penman equation can be represented graphically on vapor pressure () versus temperature () graphs (Qualls & Crago, 2020). Here, actual regional evaporation is represented graphically on (, ) graphs using the Complementary Relationship (CR) between actual and apparent potential evaporation. The CR proposed by the authors can be represented in a simple and intuitive geometric form, in which lines representing the regional latent heat flux, , and the wet surface (Priestley & Taylor, 1972) evaporation rate, , intersect at =0. This approach allows a graphical estimate of (or the corresponding mathematical formulation) without the need to know either the wet surface or the apparent potential evaporation rates. The wet surface temperature is needed, and a calculation method for it is provided. The formulation works well using monthly data from seven sites in Australia, even when the same value of the Priestley & Taylor parameter α is used for all sites.