I stumbled across this chart in Yahoo Finance some months ago. It expands the "compare to" function to include up to five stocks and indices. To generate this particular chart, for the current day and time, click here. Click on the chart to see a full size version.
These stocks are a portion of a portfolio I follow, of dividend-paying stocks. I had used the stock screener to find stocks with high dividends, then the history function to find out which of those has had stable dividends for the past decade or more. Then a tool like this allows me to pick a momentary low spot, which boosts the effective dividend yield.
I am not a day trader, but I do try to time my entry into an equity. Almost any stock will vary by 5% over a few weeks' time. Suppose I am interested in one that is very stable, and is currently yielding 5%; not only that, it has very seldom reduced its dividend despite large variations in the overall market. This makes it a good income stock. If the day the screener program showed its yield as 5.1% it was selling at $25, and has a very steady $0.32 per quarter, I'll watch it for a few days. A downturn in the market could drag it down to $22, at which point I might purchase it. The dividend isn't likely to change, but now the effective yield is 5.8%. And the company's underlying value is the same, so it'll be back at $25 before long, and may grow substantially from there.
Whether it does or not, every 100 shares purchased gains nearly 6 shares a year in reinvested dividends. Give it ten years, and I'll have 176 shares where I had 100. If the stock has also risen, that's an added bonus when I am ready to sell. By the way, I only trade stocks inside my IRA, so I don't pay ongoing taxes. The tax bill will be high enough when I take money out of the IRA anyway!