Reference Lines

Reference Lines allow you to place lines on the plot at specific locations to mark important values.  You could use these to  mark control limits or to indicate a trend line for a set of data.

Reference Lines Window

Enable Reference Lines

You may turn off all reference lines by unchecking the Enable Ref Lines box at the top of the plot.

Creating a Reference Line

Press the Insert Row button on the left side of the tool bar to insert a row.  Then double click on each cell to edit it.


This is the text that you would like to display with the reference line. It is not required and you may leave it blank. If you choose to edit it, you have a wide variety of choices in controlling the properties of the displayed text.  Click here to see the options.


This is the style for the reference line. There are six styles from which to choose.


This is the relative line width for the reference line.  The default value is 1.0.  A value of 0.5 will make the line half as wide.  A value of 2.0 will make the line twice as wide.


This is the color for the reference line.


Check this box if you would like to draw this reference line. Uncheck it if you would like remember the line, but do not want to draw it on the current plot.

Positioning the Reference Line

There are two ways to specify where the reference line should be positioned and how long it should be.  You may specify a slope and point or specify two points.

Slope and Point Method

Specify a point by entering in values in the x1 and y1 columns of the table. Specify a slope by entering in a value in the m column.  The values that you enter must be in the coordinates of the plot.  This will draw a line all of the way across the plot. Use "Infinity" for the slope to draw a vertical line. For example, to draw a vertical line at x = 2.0, enter '2.0' in the x1 column, '0.0' in the y1 column and 'Infinity' in the slope column.  Use a slope of 0 to draw a horizontal line.  For example, to draw a vertical line at y = 1.0, enter '0.0' in the x1 column, '1.0' in the y1 column and '0.0' in the slope column.

Two Points Method

This method is useful if you only want to draw a line across part of the plot.  Specify one point but entering values in the x1 and y1 columns.  Specify the second point by entering values in the x2 and y2 columns.  For example, to draw a line from (1.0, 1.0) to (4.0, 4.0), enter '1.0' in the x1 column, enter '1.0' in the y1 column, enter '4.0' in the x2 column and enter '4.0' in the y2 column.