Carpenter evidence

A carpenter was giving evidence about an accident he had witnessed. The lawyer for the defendant was trying to discredit him and asked him how far away he was from the accident. The carpenter replied, "Twenty-seven feet, six and one-half inches." "What? How come you are so sure of that distance?" asked the lawyer. "Well, I knew sooner or later some idiot would ask me. So I measured it!" replied the carpenter.