svoid video_scoreRect_x(Scorer scorer, Rect expected, Rect guessed, double tolerance) {
  if ((guessed == null) != (expected == null)) ret with scorer.addError();
  if (expected == null) ret with scorer.addOK();
  scorer.addZeroToOneError(average(
    abs(rectCenterX(guessed)-rectCenterX(expected)),
    abs(guessed.w-expected.w))/tolerance);
}