Now I see it Rated 5 out of 5 stars

I couldn't find the icon in order to use this extension but now I found it. It's in the add-ons toolbar. The keyboard shortcut to show or hide that toolbar is Control +/

This review is for a previous version of the add-on (0.4.10). 

Many thanks rbarra. I'm working on an update to make this easier on folks. Sorry for the trouble but thanks for using MeasureIt!