def round_off(idnad: Tuple[List[float], List[float]], dp: int = 2):
    """
    Round off an ideal/nadir estimate e.g. so that it's looks nicer when
    plotted. This function is careful to round so only ever move the values
    away from the contained range.
    """
    ideal, nadir = idnad
    mult = np.power(10, dp)
    ideal_arr = np.floor(np.array(ideal) * mult) / mult
    nadir_arr = np.ceil(np.array(nadir) * mult) / mult
    return list(ideal_arr), list(nadir_arr)