mfcleaner
Contrary to what's said above you can keep the arc to well within 0.1 of a DME accuracy quite easily. Checkboard & italia458 has it about right, except you need to be "wind aware" which will change the basics slightly. I wrote a DME tutorial for one of my students once, if you'd like it send me a PM and I'll see if I can find it. I am sure it's on a hard drive somewhere.
D777