From the Datum list, you can select the datum line you want to modify.

A datum line can be hidden or displayed on a plot by activating the Datum check box.

Use the drop-down menu next to the Datum check box to switch between phase and radial datum lines.

You can cut, copy, paste or add datum lines to the list.

From this tab, you can create a label for a datum line, select the datum line's location on the screen, and enter a math expression to define the datum line's location.

You can enter a single value or mathematical expression that returns a single value to position the datum line on the plot.

From this tab you can set the attributes of a datum line.  Click Use Preferences to use the preferences  defined in the preferences.mvw file.