I like the way this works but 2 suggestions. It needs a way to turn off the mark once you are finished and how about adding a command like /measure x,y,z:x,y,z so we can manually add the coordinates we want to measure.
also when I set a mark and measure it. then I log out to get rid of the mark. when I log back in and press my tab button to see who is on, everything freezes, it seems. The tab screen doesn't go away and I had to hard boot my computer to get controle again.
this happened on both my single player and my multiplayer server that is rented. had to remove for this reason. If this can be fixed I would love to reinstall the updated version. I think this could be a valuable tool.
Just added command to remove the setted mark.
Its totally to measure the distance between two points (see description).
I do not experience the issue with the tab button 
Probably you are using some other plugins which interfere with this one?
