Dimension a line that is already drawn

I have a very simple drawing

http://www.kirkbymicrowave.co.uk/Dielectric-Test-Fixture/U-channel.dxf

of basically a U-channel, which I drew with version 2.13 on Windoze.



Most of the dimension are integer multiples of 1 mm, except the depth, which should be 17.85 mm. I've dimmensioned all the lines which are multiples of 1 mm, by just picking points near the line, which is easy as the program snaps to the 1 mm grid easily enough.

But the lines which are 17.85 mm don't fall on the grid, so I can't dimension this way.

Is there any way to select a line, then add the dimension to the drawing?

Dave

Ignore this, unless you can think of a better way. Snapping to the intersection of two lines did the trick.