How do you measure the distance between two points within the viewport ortho mode? MMB not working

I imported a terrain and I am trying to scale it properly. I know the size of features in the terrain so I just want to measure it to see if I got it right. MMB + drag = no workee. I’ve tried top/left views + lit and wireframe … help me please. Surely there is an easy way to do this? Also, I am confused about the grid dimensions and meanings. The grid squares have squares in them … what are their sizes? confused. thx

MMB+Drag is working for me on 4.16

It turned out that it was Microsoft Keyboard and Mouse Setting default of task switching. I changed to middle-click and works now. thx saeedc

Yes it works, https://gyazo.com/6dbeadcc4faf2a43acd0d58ce6d2e301