Regarding the term "Spin"... I've see a number of different descriptions. In the book I'm currently reading it says it is "loosely" the measure of the strength of rotational motion, and "technically" the measure of the quantity called angular momentum. It also states we consider the spin of an photon to be 1, and electron to be 1/2, etc. My question is: Were these values (1, 1/2, 1-1/2, etc.) arrived at by some type of mathematical calculation, or were they arrived at by some type of physical measurement (using some type of measuring device)? And what does the number "1", as it relates to "Spin", mean? Does it have anything to do with the quantity of the number "1"?