def pres_units(units):
    """
    Return a standardized name (hPa or Pa) for the input pressure units.
    """
    hpa = ['mb', 'millibar', 'millibars', 'hpa', 'hectopascal', 'hectopascals']
    pa = ['pascal', 'pascals', 'pa']

    if units.lower() in hpa:
        return 'hPa'
    elif units.lower() in pa:
        return 'Pa'
    else:
        raise ValueError('Unknown units ' + units)