def _ngl_write_cell(a1, a2, a3, f1=90, f2=90, f3=90):
    """
    Writes a PDB-formatted line to represent the simulation cell.

    Args:
        a1, a2, a3 (float): Lengths of the cell vectors.
        f1, f2, f3 (float): Angles between the cell vectors (which angles exactly?) (in degrees).

    Returns:
        (str): The line defining the cell in PDB format.
    """
    return "CRYST1 {:8.3f} {:8.3f} {:8.3f} {:6.2f} {:6.2f} {:6.2f} P 1\n".format(
        a1, a2, a3, f1, f2, f3
    )