The Dow theory is a financial theory that says the market is in an upward trend if one of its averages advances above a previous important high and is accompanied or followed by a similar advance in the other average.look at minimum 2 year timeline . the best one to use for charts r line chart because it is easy to look at top and bottom which are important to do dow theory.when demand is greater or stronger than supply then buy. if supply greater or stronger than demand then sell. the trend is reliable till the pattern is intact