So... this is how my little brain had to think of it - maybe this will simplify the concept (or maybe make it more complicated). It's not just that the target is moving and thus is in a different spot than it was when the bullet left the muzzle (because the muzzle, and thus the bullet is moving also), but that the muzzle and the target are moving at different speeds. At the equator, or at least at the greatest circumference vertical to the axis of rotation, the surface of the earth is moving at about 1038 mph or a little over 1522 feet/sec. As you move away from the equator, the circumference vertical to the rotational axis becomes smaller, so the distance traveled in 24 hours becomes less - consequently, the surface speed is less. If you are shooting south to north (in the northern hemisphere), the west to east (left to right) speed of the muzzle, and hence of the bullet leaving that muzzle is greater than the west to east speed of the target, so the bullet ends up right of the target (although not by much, as stated earlier). If shooting north to south, the target is moving west to east (right to left) faster than the muzzle, so the target moves farther during the flight time, and the bullet still ends up right of the target. But until I shoot a heck of a lot better than I do now, I don't think I will need to waste time calculating surface speed differentials!!