helper function that writes the actual measurement configurations to a
    file descriptor.

    Parameters
    ----------
    fid: file descriptor
        data is written here
    quadpoles: numpy.ndarray
        measurement configurations

def _syscal_write_quadpoles(fid, quadpoles):
    """helper function that writes the actual measurement configurations to a
    file descriptor.

    Parameters
    ----------
    fid: file descriptor
        data is written here
    quadpoles: numpy.ndarray
        measurement configurations

    """
    fid.write('# A B M N\n')
    for nr, quadpole in enumerate(quadpoles):
        fid.write(
            '{0} {1} {2} {3} {4}\n'.format(
                nr, quadpole[0], quadpole[1], quadpole[2], quadpole[3]))