Error bars

[jmallen]

I want to put error bars on points in a scatter graph, with bar length +/- 10% of the value of each point.

How is this done?

[grumpychemist]

Hello hello,

this is very easy though DataGraph handles doesn’t give you the direct option to set error bars to +/- a percent. Instead it lets you set the error bars to a value of a column so what you need to do is create a column with your desired error values. You can use a function to make it 10% of the y value.

So have a look below, I have put some arbitrary x and y data into columns and then I have created a function column (the f(x) button) and typed in the formula 0.1*y_data. This creates a column which contains our 10% errors.

Now in the plot, I have gone to my points command and pressed the expansion triangle to open up all the options. At the bottom are the error bar options. Ive added small error bars and changed the error in y to the new column I created using the error function. By default it plots both the positive and negative error.

 

hope this helps.

[grumpychemist]

Hello hello,

this is very easy though DataGraph handles doesn’t give you the direct option to set error bars to +/- a percent. Instead it lets you set the error bars to a value of a column so what you need to do is create a column with your desired error values. You can use a function to make it 10% of the y value.

So have a look below, I have put some arbitrary x and y data into columns and then I have created a function column (the f(x) button) and typed in the formula 0.1*y_data. This creates a column which contains our 10% errors.

Now in the plot, I have gone to my points command and pressed the expansion triangle to open up all the options. At the bottom are the error bar options. Ive added small error bars and changed the error in y to the new column I created using the error function. By default it plots both the positive and negative error.

 

hope this helps.

[jmallen]

Thanks.

Works for points (scatter) plots.

But not for Plot/Plots which are essentially scatter plots with the points joined by straight lines in sequence.

So I have a Points plot and want to add Y error bars. How to do it?

[dgteam]

The Plot command has the same mechanism as the Points command.

By default, there are no error bars. That is set a the bottom the command.

When you select a type of error bar, the options expand so you can select the columns you want.

Here is an example with the Ellipsoid option.

The Plots command does not have error bar options.    If you prefer the Plots command for drawing lines, you can combine that with a Points command to draw the error bars.