where T is the dry-bulb temperature expressed in degrees Celsius (°C), P is the absolute pressure expressed in millibars, and e w ∗ ∗ is the equilibrium vapor pressure expressed in millibars. Buck has reported that the maximal relative error is less than 0.20% between −20, and +50 °C (−4, and 122 °F) when this particular form of the generalized formula is used to estimate the equilibrium vapor pressure of water.