def iso7064mod11_2(source: str) -> str:
    """

    iso7064mod11-2校验算法

    :param source: 需要添加校验的字符串
    :return: 校验位

    """
    sigma = 0
    size = len(source)
    index = 0
    for i in source:
        weight = (2 ** (size - index)) % 11
        sigma += (ord(i) - 48) * weight
        index += 1
    sigma %= 11
    sigma = ((12 - sigma) % 11)
    return "X" if sigma == 10 else chr(48 + sigma)