Dryer,

Thanks so much for your post as it stimulated another idea and it's something I've never heard before. Deductive reckoning isn't just map and compass. It's using everything to narrow down a position.

Situation: You passed a draw and then maintained a pretty constant altitude while on a bearing of 102 MN for 817 feet. Then you find yourself at the end of a spur. The bearing up the ridge of the spur is 243 mn. You are at 7,400 feet. Where are you?

7,400 feet gives a Line of Position (LOP). The vector 102/817 rules out most of that line. The bearing up the spur nails it.