Why is the sky blue, rateliff.
This is a peculiarity of CRT (cathode ray tube) monitors. The viewable area is always 1-1/2 inches less than the actual size. Thus, your 20 inch monitor comes up a little short when you actually take a ruler to it.
LCD monitors don't have this problem. A 15" LCD is exactly 15 inches corner to corner, almost exactly equivalent to a 17" CRT, which is 15.5".
