I type DI on the command line then pick two endpoints to list a distance in AutoCAD. This distance is 3D, a slope distance. How do I get a horizontal distance? Set the System Variable, OSNAPZ to 1 then use the DI command.
I could tell you all about OSNAPZ but then you would not develop the skills to look up information on your own in the AutoCAD help file. (Remember, the theme of this blog is to improve your skills.)