def calc_check_digit(number):
    """Calculate the check digit. The number passed should not have the
    check digit included."""
    weights = (3, 7, 13, 17, 19, 23, 29, 37, 41, 43, 47, 53, 59, 67, 71)
    s = sum(w * int(n) for w, n in zip(weights, reversed(number))) % 11
    return '01987654321'[s]