True, the rule is measured in seconds. But, I can't accurately measure time without distance. If a car passes a pole at time = 0 at ~ 60mph, I will be a certain

True, the rule is measured in seconds. But, I can't accurately measure time without distance. If a car passes a pole at time = 0 at ~ 60mph, I will be a certain distance behind the car if I pass the pole 2 seconds later, traveling at approximately the same speed. I find it a little easier to use distance to maintain this over time, because I can always see how far ahead of me the car is, but to measure by time takes landmarks and it's much harder to get a real accurate time measurement. In any case, I tend to err a little on the high side regarding distance for this reason.