Jet-mouse - I'm with you. Always managed to get differing answers to books. Even the exam papers had errors in them!! . .. .IN my case my CFI once pointed out to me - in the real world, if you can fly within +/- 3 degrees in an R22 that's shaking the fillings out of your back teeth, your doing well. <img border="0" title="" alt="[Wink]" src="wink.gif" /> . .. .Good luck with the rest of your maths.