def perc_bounds(percent_filter):
    """
    Convert +/- percentage to decimals to be used to determine bounds.

    Parameters
    ----------
    percent_filter : float or tuple, default None
        Percentage or tuple of percentages used to filter around reporting
        irradiance in the irr_rc_balanced function.  Required argument when
        irr_bal is True.

    Returns
    -------
    tuple
        Decimal versions of the percent irradiance filter. 0.8 and 1.2 would be
        returned when passing 20 to the input.
    """
    if isinstance(percent_filter, tuple):
        perc_low = percent_filter[0] / 100
        perc_high = percent_filter[1] / 100
    else:
        perc_low = percent_filter / 100
        perc_high = percent_filter / 100
    low = 1 - (perc_low)
    high = 1 + (perc_high)
    return (low, high)