Crispy wrote:

Agreed. That "mAD" notation is the most stupid thing I've ever seen from a maths textbook (and believe me when I say I've seen some boneheaded things in maths textbooks).

I would like to introduce whoever dreamed up that nonsense to my Calculus textbook, by way of an overhead swing. Given the size and weight of that textbook, this is no small threat. ;-)

The mAD notation is more useful when proving something. It means the measure of AD. There's some sort of distinction (that I can't remember at the moment) between stating that two angles (or lines, etc) are equal?/congruent?, and stating that their measures are equal.