The QtiPlot Handbook
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# Add Error bars

This dialog is activated by selecting the Add Error Bars... command from the Graph menu.

This command is used to plot X and/or Y error bars around the data points.

It must be taken care that the "add" button add the errors bars, and so do the "OK" button. Then, you should close the dialog with cancel if you have clicked on the "add" button.

Figure 5-2. The Add Error Bars... dialog.

There are three ways to specify the size of the bar:

A column of the table

  In this case, the values of the selected column are used to compute the error bars. if V is the value of the data point, and E the value of the errorbar column, the size of the bars will be V-E to V+E.

A percentage of the values

  if E is the percentage selected, the size of the bars will be V(1-E/100) to V(1+E/100). It must be noticed that, in addition to the errorbars on the plot, this command will create a new column in the active table with can be used in the way as with the previous option. This column can be modified like any other one.

The standard deviation of the values

  the standard deviation of the values. This has a meaning only of the data are centered around an average value. Like with the previous option, a new column will be created in the active table.

Figure 5-3. A plot with X and Y Error Bars.

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