The Apple Characteristic component is classified as an 'Impedance Zone Element', which checks whether or not a point described by inputs R and X, lies inside a specified region on the impedance plane. R and X represent the resistive and reactive parts of the monitored impedance, and may be input in per-unit or ohms. Please note however, that the units of the component input parameters should match that of the R and X inputs. The component produces an output '1' if the point defined by R and X is inside the specified region, otherwise the output will be '0'.
An apple characteristic can be formed using two circles with equal radius, and is defined as the union of the two circles.