Vermesse what you want!
How does this work?
Go to the start point and press ALT + right-click. Now, the starting point is set and display the distance on your screen (center bottom). Over now to the end point of your measurement. The distance between yourself and the starting point is always displayed. Height differences are taken into account.
What do I mean?
Well, you could measure your yard. Or meaningful to do, how to cut trees after cutting to length)
ALT + right click => sets or clears the starting point