The string thing was an absolute winner for formation split tac navs in RAAF helicopter days.
You'd mark your string (non-stretchy, of course) in nil-wind minutes at 90 kts (using 1.8km = 1nm) and from then on the exercise area was your oyster - pick a split and an RV point, then lay out the string in whatever squiggly path took your fancy, marking the minutes out on the route with chinagraph ('Contact' covered map - I guess that's the same as what you blokes call fablon?).
Then, keeping the start and end points of the string in place, move it to make another route of exactly the same length - easy to see the crossing points / conflicts, if any, and very very simple to work back from a time-on-target.
As good as a computer any time, if not better than, I reckon.
Last edited by Arm out the window; 18th Nov 2012 at 23:14.