The Automatic pitch change option is the standard option for accounting for pitch change between components. The pitch ratio is taken to be the ratio of the interface areas of the two components. The two sides must each have the same radial or axial extent and can therefore only differ in extent in the direction of rotation of the frame of reference. This means that the surfaces on each side of a frame change interface must sweep on the same surface of revolution. But in case there two interface sides has different radial extent then “Automatic” option should not be used because it will calculate incorrect pitch ratio from area ratio. In those kind of models either set the true pitch ratio using (one number is entered, code automatically sorts out the polarity ie. with ratio can be either smaller or bigger than unity) or you can manually give the pitch angle for each side of the interface.