Reading Values from Graphs

When creating charts from Excel data, you can smooth out the lines between data points by using any number of methods. At some point, you may want to actually figure out how Excel does its calculations to determine where to actually plot points along the line. Rather than visually trying to figure out where a point falls, you can follow these steps:

1. Right-click on the data series in question. Excel displays a Context menu.
2. Choose the Add Trendline option from the Context menu. Excel displays the Add Trendline dialog box; in Excel 2007 it is the Format Trendline dialog box. (Click here to see a related figure.)
3. Make sure the regression type you want to use is selected.
4. Display the Options tab. (In Excel 2007 it is the Trendline Options tab.)
5. Make sure the Display Equation on Chart check box is selected.
6. Click on OK.

The result is that Excel shows a formula, on the chart, that represents how it calculated each point along the line. You can then use this formula to determine points, as well. No more guessing! Once you know the formula, you can turn off the formula display if you want it off.

If you would like to know the different formulas that Excel uses for different types of trend lines, you can use the online Help system to search for "equations for calculating trendlines."