def calc_checksum(arr: bytearray) -> int:
    """Calculates a 2 byte sum of the byte array ignoring rollover.

    Parameters
    ----------
    arr : bytearray
        The full range of bytes that the checksum should be calculated on.

    Returns
    -------
    int
        The checksum of the bytes.
    """
    return sum(arr) & 0xFFFF