How to make a line measurement

How to make a line measurement:

Select any Grid overlay in the overlay menu.
Select the measuring tool icon (signified by a ruler) in the overlay menu, located between the zoom buttons and the overlay icons.
Select the Line Measurement option (signified by a line icon) at the top of the measuring tool window.
Click on the location in the 3D world where one end of the measurement line should be placed.
Click on the location in the 3D world where the other end of the measurement line should be placed.
The graph in the measuring tool window now displays the values along the placed measurement line.

Notes

Note that when using a line measurement, the displayed values are only the values found along the line at the Timeframes (Water Overlay) currently displayed by the Grid overlay.