The Ruler tool can be accessed in the toolbar at the bottom right of the GAme Board, regardless of mode. It is a simple tool that gives you the option to measure distances.
From the place where you clicked a line is drawn with a number showing the distance to your mouse cursor, until you release the mouse. It shows the first decimal to support using the metric system with games that were devised with the imperial system in mind (e.g. the standard 5-ft grid in D&D translates to 1.5 m).
If you turn on the
Share with others option that opens up above the
Rulerbutton in the toolbar, this will be publicly visible for all players in the session.
If you turn off this option, only you will see the ruler.