The Measure Distance () action is available from some plot windows (Plane, Histogram, Sky, Corner and Time plots). This allows you to use the mouse to measure the distance between two points on the plot. To use it, first click the Measure Distance toolbar button or menu item, and then press the mouse button on a point in the plot from which you wish to measure, and drag the mouse, holding down the button, to the point you wish to measure to. As you drag the mouse, the distance(s) between the two points are displayed and updated interactively. Once you release the mouse button, measurement mode is exited, and you need to invoke the action again to make another measurement.
Measuring distance in the Plane Plot
The details of what distances are displayed depends on the plot window in question, according to what metrics are defined on the plot space. For the Sky plot, the shorter great circle arc is drawn on the plot between the two points, and the distance is labelled in degrees, minutes or seconds. For the Histogram and Time plots, vertical and horizontal components are drawn and labelled in terms of the distances along the corresponding axis. For the Plane plot, both components and the direct distance are measured.