def ms_300_to_od(ms):
    """Convert the milliseconds to score a 300 into an OD value.

    Parameters
    ----------
    ms : float
        The length of the 300 window in milliseconds.

    Returns
    -------
    od : float
        The OD value that produces a 300 window of length ``ms``.

    See Also
    --------
    :func:`slider.mod.od_to_ms_300`
    """
    return (ms - 79.5) / -6
