This plot is the conclusion of a problem I've just completed. It describes how the temperature varies at very small distances above a surface in some sort of flow. Pr is the Prandtl number which is the measure of a fluid's viscous diffusion to it's thermal diffusion. (For a point of reference, Pr for air is around 0.75, while for molten metals it's on the order of 0.1 and lower). The computer code that I wrote to produce this plot worked flawlessly on the first try. It's a good thing when you do things right.