Seeing historical stock prices graphed over time shows you trends in a stock's performance. Past performance doesn't necessarily predict what the stock will do in the future, but it can help you decide when to buy or sell. A stock chart or graph can also highlight repeating patterns in the price movement -- knowledge you can use to make future trades.
Copy or download historic prices for a stock, along with the dates the prices occurred. Yahoo! Finance (finance.yahoo.com) provides free individual stock data going back to 1970, and Google Finance back to 1978. After looking up a stock on either site, click the "Historical Prices" link and input the date range you want historical prices for.
Create a new sheet in your spreadsheet program. If you don't have one, OpenOffice.org provides one for free.
Input the historic dates Column A and the associated closing price for that day in Column B. The closing price is the last transaction of the official trading session; it's the most important price of the day, representing the final consensus of value for the stock.
Select the data in column A and B that you'd like to graph.
Insert a line graph from the charting options in the spreadsheet. Typically this is under the "Insert" heading. The dates will automatically appear along the x-axis, which is the bottom of your chart; the prices along the y-axis, or the vertical side of the chart. Right-click on the chart to modify its characteristics.
Interpret the chart. If the price is moving in an overall upward direction, the trend is up. If the price is moving in an overall downward direction, the trend is down. The trend shifting from down to up is traditionally a buy signal; an uptrend changing to a downtrend is a signal to sell.
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