At least two old-time grain traders I know swear by this, and you should check it out.
The story goes like this: There was a millionaire grain trader who had three children. After their mother died, he raised them by himself and dedicated his life to his children. But the children were lazy and thought they would inherit all the money. He thought his children wasteful, and believed they took him for granted. When he died, all the money went to charity. All he left them in his will were the following dates of when to buy and when to sell. The will indicated that if they strictly followed his advice (shown as follows), they would have the fortune they always thought was going to drop in their laps:
Sell March wheat ...