Error bars express potential error amounts that are graphically relative to each
data pointIndividual values plotted in a chart and represented by bars, columns, lines, pie or doughnut slices, dots, and other shapes called data markers. Data markers of the same color constitute a data series.
or
data marker A bar, area, dot, slice, or other symbol in a chart that represents a single data point or value that originates from a cell on a sheet. Data markers of the same color constitute a data series.
in a
data seriesA group of related data points plotted in a chart that originate from rows or columns on a single sheet. Each data series in a chart has a unique color or pattern. You can plot one or more data series in a chart. Pie charts have only one data series.. For example, you could show 5 percent positive and negative potential error amounts in the results of a scientific experiment. You can add error bars to data series in a 2-D area, bar, column, line, stock, xy (scatter), or bubble chart. For xy (scatter) and bubble charts, you can display error bars for the x values, the y values, or both.

Do any of the following:
 | Express errors as a percentage, standard deviation, or standard error |
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On the View menu, click Print Layout.
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In the chart, select the data series that you want to add error bars to, and then click the Chart Layout tab.
For example, in a line chart, click one of the lines in the chart, and all the
data markers A bar, area, dot, slice, or other symbol in a chart that represents a single data point or value that originates from a cell on a sheet. Data markers of the same color constitute a data series.
of that
data seriesA group of related data points plotted in a chart that originate from rows or columns on a single sheet. Each data series in a chart has a unique color or pattern. You can plot one or more data series in a chart. Pie charts have only one data series.
become selected.
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Under Analysis, click Error Bars.

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Do one of the following:
Click | To |
---|
Error Bars with Standard Error | Apply the standard error, using the following formula: 
s = series number
I = point number in series s
m = number of series for point y in chart
n = number of points in each series
yis
= data value of series s and the Ith
point
ny
= total number of data values in all series |
Error Bars with Percentage | Apply a percentage of the value for each data point in the data series |
Error Bars with Standard Deviation | Apply a multiple of the standard deviation, using the following formula: 
s = series number
I = point number in series s
m = number of series for point y in chart
n = number of points in each series
yis
= data value of series s and the Ith
point
ny
= total number of data values in all series
M = arithmetic mean |
| |
 | Express errors as custom values |
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On the View menu, click Print Layout.
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In the chart, select the data series that you want to add error bars to, and then click the Chart Layout tab.
For example, in a line chart, click one of the lines in the chart, and all the
data markers A bar, area, dot, slice, or other symbol in a chart that represents a single data point or value that originates from a cell on a sheet. Data markers of the same color constitute a data series.
of that
data seriesA group of related data points plotted in a chart that originate from rows or columns on a single sheet. Each data series in a chart has a unique color or pattern. You can plot one or more data series in a chart. Pie charts have only one data series.
become selected.
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Under Analysis, click Error Bars, and then click Error Bars Options.

If you see the Add Error Bars dialog box, select the series that you want to add error bars to.
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In the navigation pane, click Error Bars.
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Under Error amount, click Custom, and then click Specify Value.
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Switch to Excel.
When you switch to Excel, the Custom Error Bars dialog box appears.
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In the Positive Error Value and Negative Error Value boxes, type the values that you want for each data point, separated by commas (for example,
0.4, 0.3, 0.8), and then click OK.
 | Note You can also define error values as a range of cells from the same Excel
workbook. To select the range of cells, in the Custom Error Bars dialog box, clear the contents of the Positive Error Value or Negative Error Value box, and then select the range of cells that you want to use. |
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Switch to Word.
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In the Format Error Bars dialog box, click OK.
 | Add up/down bars |
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On the View menu, click Print Layout.
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In the chart, select the data series that you want to add up/down bars to, and then click the Chart Layout tab.
For example, in a line chart, click one of the lines in the chart, and all the
data markers A bar, area, dot, slice, or other symbol in a chart that represents a single data point or value that originates from a cell on a sheet. Data markers of the same color constitute a data series.
of that
data seriesA group of related data points plotted in a chart that originate from rows or columns on a single sheet. Each data series in a chart has a unique color or pattern. You can plot one or more data series in a chart. Pie charts have only one data series.
become selected.
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Under Analysis, click Up/Down Bars, and then click the up/down bar that you want.

Depending on the chart type, some options may not be available.