ORIGINAL: GregH
Practice, practice and more practice!
I estimate tine length based on ear length, an ear being roughly 6 inches.
Inside spread based on tip to tip ear length. 16" for 2 1/2s, 17" for 3 1/2s and 17'-18" for 4 1/2s and older.
Mass and beam length are estimates that are ingrained in my head from the many deer I've actually measured. So it's a best guess for me.
I tend to slightly underestimate deer. I guess that could be good. LOL I usually don't give them enough credit on main beam length.