Cody - I agree that your "Red" measurement system should be the only system due to a couple resaons. Most people who shoot a rifle with a lot of drop at the heel and toe think they need 14" (or more) of pull in order to shoot the rifle comfortably, then inocently and mistakenly think this applies to every rifle they come across. Problem being that the straighter the stock, the shorter 'pull' one 'needs'. Most people don't understand this.
This is why you get guys thinking they need 14 1/2", I these are guys who have a 30" arm, short necks and measure in the 'short' range for height. ('short range' is anything in the 5' whatever range BTW - yes I'm opinionated - but do it honestly
)
Never fails that someone at some time, on about any gun forum there is eventually posts a thread asking "What's your length of pull?" This one s really funny in the responses due to the '@#$$%&* match' that invariably results. I've seen guys edit their responses every time someone lists a longer length of pull than what they originally posted.
As I said, length of pull desired by an individual varies with the shape of the stock - if measured from the trigger to centre of the butt ie: blue line, but varies little when measured trigger to centre of the butt on the line of the bore - ie: red line.
One other aspect of length of pull is that an experienced shot can use a variety of lengths of pull equally well in accuracy, but someone who 'needs' a certain length of pull usually is quite easily beaten at the game and actually needs a LOT more practise to become proficient.
So, what's my length of pull? - it's 26" to 29" depending on the 'stick' I'm shooting, and then it varries from 29" to 32" - whatever the compound bow demands. Oops, rifles - that would be from about 13" to 15" depending on drop and whatever the rifle happens to have.
It is easy to shoot a stock that is shorter than you'd prefer, but difficult to shoot a stock that's too long.