Fancy & pretty rulers etc. when needed in a hurry are probably on the seat in your bag, or dropped on the floor !
Moreover they need knowing well enough where to look for one's 'easy' answers. The one above has several speeds to suit many a/c, but in one's usual mount each 1/2 mill. chart inch is 8 nm. Thus at 80 kt takes 6 minutes.
Double speed e.g and 3 min's. So half way between 120 kt = 4 1/2 minutes.
TBH in my a/c I simply multiply miles distance to go X 7 which suits its pedestrian 80 and a bit speed.
Same idea for simplifying direction adjustments corrections, as several before me have recommended, and the '1 in 60 rule' is quite accurate really.
Measuring off the chart, one inch in my case is a thumb width,
Now you can't easily drop that on the floor !
Ground speed/drift etc. is naturally a component, but if not a hooley blowing, map reading and small course corrections works: as does marking the chart where you know you really are at every useful ground feature or each 5 minutes as you wish - then with a good eye & if temporarily uncertain of position, your time and heading since last fix is pretty useful.
mike hallam