This calculator uses the method described by A. G. Okkes in Hydrocarbon Processing, dated July 1987, pp 53-55. The SO3 conversion from SO2, if calculated, is assumed to be set by equilibrium at 1000 °C. The flue gas is assumed to be at atmospheric pressure. A deviation of 200mm H2O will result in a 0.4 °C error in the predicted dew point.