Kirsty it was my instructors advice and i found it worked for me. To reinforce the reasoning, try doing dead reckoning the RAF way! They use an advanced DR technique called the IP technique. This involves picking a very prominent grond feature, something that is easily recogniseable from low level. No guesses as to why that particular requirement is necessary! This feature should be within 20 minutes of your target. Then using 1/4mil charts and OS maps, plan your route from said IP (initial point) to target in a STRAIGHT line. Mark off at five mile intervals and fly at a speed which is a multiple of 60. This makes it easy to compute eta, eg- 15 miles to run? 7.5 mins at 120Kn or 10 mins at 90Kn. Concentrate on flying THE NUMBERS and you WILL arrive at the target on time. The reasoning is obvious, its not too challenging to fly accurate NUMBERS for a period of 15 - 20 mins after finding the IP. So in summary, they fly numbers as it may not allways be possible to find suitable ground features every 10 miles! Think desert or sea
