About E-Shield transformer construction

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In old designs, flux band and the bias winding between primary and secondary was the usual techniques for improve EMI. It was easy to understand how these techniques work. Now we have several windings working like electrostatic shields, and it isn't easy for me to understand how they work I'd like to known how core cancellation & balancing shield windings work, and how PIExpert calculate the number of turns. Thank you very much for your assistance.
Please take alook at http://www.powerint.com/en/community/documents-quizzes/puzzler-8#answer3 for explanation on the shileds to improve EMI