def clean_minmax(dic):
    """
    Clean (set to zero) the MAX/MIN dictionary keys.
    """
    # maximum and minimum values
    dic["FDMAX"] = 0.0
    dic["FDDISPMAX"] = 0.0
    dic["FDMIN"] = 0.0
    dic["FDDISPMIN"] = 0.0
    dic["FDSCALEFLAG"] = 0.0    # FDMIN/MAX not valid
    return dic