Preparation of the chart itself is important too.
fwiw my technique was this. Buy unfolded charts. Trim the borders off the chart to leave the lat/long on the extreme edges (simply to reduce its size to minimum) and fold it in half along the long axis, printed surface outwards. Keeping the first long fold in place, fold in half along the short axis. Without moving the chart now halve each of the resulting panels by folding them back so the ends meet at the centre fold. You now need to think a moment which way you need to fold each resulting (keeping the original long-axis fold in place all the time) to halve them too, and you'll end up with a fanfold. The folded chart will now be 1/16th the area of the original, 8 panels on each side. This is small enough to have two panels open at the same time if needed and can be further loosely folded in half acrossways in the air without putting a crease in it. This makes manipulating even a half Mill a one-handed job.
If my description doesn't make sense follow it through on a piece of A4. Believe me, its worth the effort. This works with any chart thats more or less rectangular, 50,000 (helilanes) 250,000 and 500,000. If you need the crib cut it out and stick it on the back where it doesn't interfere with the folds, and magic mark the edition number and date on the back too if that came off with the border. There's no reason why you can't vary the number of folds - a six panel fold is not so easy but perfectly doable if it gives you a better panel size. Up to you.
Pens. Wax crayons are a pain. Use Staedtler (?) Lumocolour indelible overhead projector pens. Solid dense ink, stands out well, colour available if you want to use them, won't rub off by mistake. Comes off with a wipe of meths and a rag. (from plastic faced charts of course!)
Hope this helps.
Last edited by Agaricus bisporus; 17th Dec 2012 at 17:41.