Quote Originally Posted by johnnywalker View Post
I believe a rule of thumb is to go with the length of the hypotenuse for "normal". The hypotenuse of 4" by 5" inches is 6.4 inches, or 163 mm. By that measure, 180 mm would be a trifle on the long side.
And now I know why Barry got scared about complexity. You just had to bring up the hypotenuse, didn't you!