Please Note: This article is written for users of the following Microsoft Excel versions: 2007, 2010, and 2013. If you are using an earlier version (Excel 2003 or earlier), this tip may not work for you. For a version of this tip written specifically for earlier versions of Excel, click here: Reading Values from Graphs.

Reading Values from Graphs

by Allen Wyatt
(last updated July 25, 2015)

4

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 if you are using Excel 2007 or Excel 2010:

  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 Format Trendline dialog box. (See Figure 1.)
  3. Figure 1. The Format Trendline dialog box.

  4. Make sure the regression type you want to use is selected.
  5. Make sure the Display Equation on Chart check box is selected.
  6. Click on OK.

If you are using Excel 2013, the steps are different only in that Excel uses the task pane instead of a dialog box:

  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 Format Trendline pane at the right side of the screen. (See Figure 2.)
  3. Figure 2. The Format Trendline task pane.

  4. Make sure the regression type you want to use is selected.
  5. Make sure the Display Equation on Chart check box is selected.
  6. Close the task pane.

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."

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (10698) applies to Microsoft Excel 2007, 2010, and 2013. You can find a version of this tip for the older menu interface of Excel here: Reading Values from Graphs.

Author Bio

Allen Wyatt

With more than 50 non-fiction books and numerous magazine articles to his credit, Allen Wyatt is an internationally recognized author. He is president of Sharon Parq Associates, a computer and publishing services company. ...

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What is 3 + 2?

2016-09-12 09:21:29

Rogério Fernandes

Hi,

I need to display in a chart, the values or at least the final value of a trend line. Maybe using a second line (blank). Can you help me with this?

thanks
RF


2015-07-27 05:54:39

DaveS

Yes, that seems to work OK. The LINEST function needs to be applied as an array formula. For a 4-term polynomial y=ax^3+bx^2+cx+d, define dynamic named ranges for Y data column (say, YRange)and X data column (say, XRange), then enter the formula

=LINEST(YRange,XRange^{1,2,3}) in a spare cell (say, H9)

Drag formula horizontally across three more cells (say, to K9)

While these cells are highlighted, press F2 function key, and then while still highlighted press Ctrl-Shift-Enter

This then returns the coefficients (H9=a, I9=b, J9=c, K9=d), which you can use in another formula to recalculate Y for a given X as you add more X,Y data.


2015-07-27 05:16:01

DaveS

For a polynomial regression line the LINEST function can be used to determine the coefficients independently of the chart. I've not tried it, but in principle you could define dynamic named ranges for the X and Y columns (to allow for adding more data), and use these in the LINEST function to automatically recalculate the coefficients as more data is added.


2015-07-25 12:47:02

Erik Oberg

If you want to use Excel's curve fit formula in your own calculations, I recommend showing more significant digits - maybe 10 or more - for best results. If you just use the formula as Excel displays it by default, it will likely yield inaccurate results. As a check, add your calculated points to the graph. If they don't fall exactly on the fit curve, it is a result of the rounded formula values; increase the number of significant digits displayed and try again.


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