Dow theory tells us to follow the trend by identifying the demand and supply zones using price and volume for a period of 2 years (daily charts)
It is useful for deriving the trend but not for buy\sell positions for short duration or intraday. It can be used for traders who trade on a monthly basis.
HB-HT with volume & LT-LB with volume derive buy and sell trends respectively.
Support – low
Resistance – high