I draw your attention to dates. Gann on page 25 of his 1929 annual stock forecast - reprinted at the back of his 'The Truth of the Stock Tape and Wall Street Stock Selector' book, states:

Start of quote:
March: 10th to 11th, very important for change in trend; 21st to 22nd important; 28th to 29th another very important date for change.
April: 3rd, 9th to 10th, 13th to 15th, 21st to 23rd.
end of quote.

Have a look at the Dow chart (eg. at barchart.com). March high 8/9th, low March 22. Observe the large movement 3rd April. 50% up prior into the 2nd, bottom on the 4th. How about that! Volatility brings out the best in Gann dates. The gann book was written in 1927, gann's forecast for 1929, above was put out late 1928 (and proved presciently accurate) and the dates he identified year after year keep on working, helping us identify key times for market changes of trend, before they occur.