The distance calculation tool lets you measure distances between points on any map in LMA. To open the tool, left click anywhere on the map, then select Functions>Distance Calculation (PolyLine).
These distance tools should appear in the top left.
Use the left button to start a new distance measurement, then click the points you want to measure on the map. If you make a mistake, use the blue arrow button to go back.
To end a measurement chain, left click anywhere on the map. When you are completely done with the measurement tool, click the red close button to close.