Have a look at this (I know you know what a protractor is but bear with me)
http://i00.i.aliimg.com/img/pb/474/9...960474_748.jpg
All the current protractors other than the stock one, are fixed so that 0 is always north. If you are traveling at say, 326 then a bearing of 0 is not north so here is the root of the issue.
Now remember those rotatable mods, like the attack wheel, the scope wheel, the rotating slide rule, all those.
Now picture that first image being rotatable in the same way those other mod tools are so that you can rotate that 0 to match your 326 degree heading. Now you can read any bearing directly on the map without having to use the stock protractor and without having to transform or do mental maths. You look at that rotatable and you have your bearing immediately.