Guidelines no longer measure things like they used to. Is there a setting that I am missing?

Way back in X4 (which I continued to use until recently), I could select (Shift-click) 2 guidelines and the distance between them could be seen in the box at the top. Now with 2018, that doesn't work and can not find any settings that allow it. The box just remains grayed out. This is causing a great deal of pain over here because this function is badly needed. I played with the dimensioning tool but it doesn't really take the place of the function that I seem to have lost. Can anybody please help?