I'm finding a straight edge yields a better line -- there's usually a checklist on board that will do the job
-- however I have been informed the flight test criteria disallow rulers and straightedges.
As for distance without a ruler handy, after you hold the pencil against a VOR rose for heading, line it up against a longitude line and read off the nautical miles from the scale -- there's 60 nm / degree of latitude.
Does
not work with latitude lines as minutes of latitude = nm only at the equator; so, make sure you know which is which
I have a mini-binder with plastic pockets inside; so, after marking and measuring the line, I stuff the map inside and note times with a grease pencil. Saves wear and tear on the map.
Yesterday as we were doing a bunch, I circled the to and from spots on the plastic and freehanded a line between the two.
Reviewed diversions yesterday between 600 and 800 AGL over nondescript snow covered countryside and cloud that did not allow for much more altitude. It was a good day for that kind of practice although we did get into some heated discussions over the minutiae of map reading. The ceiling was low but vis was 15 sm if you could get high enough to see that far.