The present invention provides a method for determining information for an air vehicle including the steps of providing a first coefficient of pressure data point, providing a situation involving the air vehicle, deriving pressures during the situation and deriving a second coefficient of pressure data point from the pressures derived during the situation, and defining a line passing through the first and second coefficient of pressure data points, whereby a selected coefficient of pressure data point on the line corresponds to the information. The invention encompasses apparatus for accomplishing the method. In some embodiments, the information relates to angles from zero lift and/or zero yaw.