This is the Cycle Period indicator described in Chapter 9.  It may be used to measure the Dominant Cycle period.

PriceIn = defaults to Close but change to the Price indicator to match the book

alpha = defaults to 0.07 as described in the book

For more information on this indicator, refer to Chapter 9 of "Cybernetic Analysis for Stocks and Futures" by John Ehlers, Publisher: John Wiley & Sons; (March 19, 2004), ISBN: 0471463078.