JStark: On marginal bulls it can be especially tough. Generally its 10" between the eyes on a moose, so you can visually do multiples of that and estimate the spread. Also, the mid 40" bulls generally appear as a real step down in size from a solid 50"+, kindof like the difference in a nice 6 point buck and a very solid 8 point. But its tough, and can go either way; a bull with big palms but short tines looks bigger, and one with skinny palms can have an odd long point on either side that makes it legal. Also, if they have 3 brow tines on a side they are legal, and counting them and determining what is a brow tine and what is an "other" tine is another whole discussion ! What you hope for is a lot of time to look him over and good visibility i.e. no obscuring brush etc.
Oneshot - Wow, thanks, I'm very flattered !