This is from the technical analysis book I am reading, please help understanding this chart. I cant get how they created this chart and cant understand it.
Quote from the book for the chart
Figure shows the profile of the 3.5-year cycle in the Dow Jones Industrial Average. The cycle is tracked in terms of six-month percentage rates of change in closing prices. Each beat of the cycle inevitably varies in terms of time elapse from the average, so the shorter cycles have been mathematically stretched to match the time elapse of the longest cycle in the matrix. Then, 18 beats of the cycle – starting in November 1946 and ending in February 2009 – have been averaged together and compared with an ideal cycle.