I think it should be useful to configure more than one unit of measurement in a map, and being able to switch freely between them as a player. The reason for this is that many players are not English-speaking, so it might be easier for them to use the metric system instead. I'll show an example of that: Pathfinder's handbook is translated into Italian, so many Italian players using those resources will often use meters, but some of them could use online resources and use feet. Handbooks also provide an approximation of units: moving from a square to an adjacent one costs 5ft. while in meters it costs 1.5m. This system could also be used to trace not only measures but also some other "game resource" that players may consume while moving, but this may create some problems depending on how diagonals are measured. A way to implement this could be: Let the GM set more than one unit of measure for each map and for the entire game, using game settings. Let the player choose which units should be shown in the ruler tooltip, based on the units available in the map The GM interface on map (page) settings could be like this:
