A witness to an automobile accident was testifying. The following exchange took place between the lawyer and the witness:

The lawyer: "Did you actually see the accident?"

The witness: "Yes, sir."

The lawyer: "How far away were you when the accident happened?"

The witness: "Thirty-one feet, six and one quarter inches."

The lawyer (thinking he'd trap the witness): "Well, sir, will you tell the jury how you knew it was exactly that distance?"