As in name Dow theory was derived by Mr Charles H.Dow.
It helps to determine the market trend for upcoming months by analysing two or more than two years of data. There are three trends
Primary trend – It can last more than a year also known major trend.
Secondary trend- Correction period of Major trend it can last up to 3 weeks to 3 months.
Minor trend – Price variation in short span of time usually lasts from few hours to few days.
Overall Dow theory used for long term investments.