In the Civil War, marksmen used something called a "stadia" which is nothing more than a piece of brass with a triangular hole cut out and a slide with marks of varying distances. Line your target up within the hole, center the slide over it, and you have the distance you need to make your shot more accurate.
http://i.ytimg.com/vi/FwGDPhNhXhg/maxresdefault.jpg Example of a brass stadia.
I, however, am not a student of math, algebra, nor trigonometry.
If I hold the Stadia at arm's length (30.5 inches away from my eye) and sight a deer that stands on average at 3.9 feet tall at 100 yards away, what is the relative height of the deer on the stadia?
