 Twiddle factors continuously correct the position of the samples in your signal so that they are ready for the next stage of the FFT. But how are they calculated? A twiddle factor is denoted by a large W followed by a superscript number and a subscript number. The superscript number tells us the index of the twiddle factor, and the subscript number tells us the order of the twiddle factor. The index and the order are substituted into a complex cosine and sine expression as follows. The cosine of 2 pi times the index over the order minus i times the sine of 2 pi times the index over the order. Evaluating this expression gives us the complex value of the twiddle factor. Multiplying the previous stage's results by this twiddle factor shifts its phase so that it is in the correct position for the next stage of the FFT.