Arc discussed on Dunnunda Thumb Rules thread, inter alia. From that discussion... one in sixty works well.
On a sixty mile arc, you change bearing one degree per mile flown.
30DME arc, two degrees per mile,
20DME, three per mile
15DME, four per mile
12DME, five per mile
10DME, six per mile
9DME, seven per mile
8DME, eight per mile
7DME, nine per mile
6DME, ten per mile
Less than 5DME, write a complaint to the issuing agency, because it is too small.
Anything in between, interpolate because you will be bloody close.
Also note that if your RMI is marked in 5 degree increments, each mark on a 12DME arc represents a mile flown/to fly. If you are incorporating a descent profile like 3nm per 1000 feet to lose, that is 1000 feet per three divisions on a 12DME arc.
With numeric skills like that, you think my countrymen could do something about the aussie dollar. <sigh>.
[This message has been edited by ITCZ (edited 10 April 2001).]