I'm guessing that the reason that the vertical height is 31 instead of 32 is that having the vertical height be an odd number makes it possible to vertically ce

I'm guessing that the reason that the vertical height is 31 instead of 32 is that having the vertical height be an odd number makes it possible to vertically center a number of important symbols, such as +, -, >, arrows, circles, X's, and so on.