The Dow theory is a theory which guides us to identify the market trend & supply, demand zones. it is an upward/bullish trend if its advances above a previous important high price and is in bearish trend when it fails to cross previous tops & bottoms.
Line chart, daily basis with duration of 2 years is considered to identify and forecast Dow Theory.
If price crosses the Higher top & higher bottom in sequential order then it is a bullish trend. If price fails to cross the previous lower top & lower bottom then it is a bearish trend.
As per Dow theory, one should buy the stock immediately it crosses the previous higher top with high volume & sell the stock when it fails to cross the previous lower bottom. it is reliable for 2-3 months.
Dow theory remains correct/precise to identify the market trend even after 100 years which makes it to top of any analysis.