def get_unit(scale):
    """
    Convert scale term to unit label
    """
    scale2unit = { 1e-9: 'nm',
                   1e-6: u'\N{MICRO SIGN}m', #or hex id (lookup): u'\u00B5'
                   1e-3: 'mm',
                   0.01: 'cm',
                   0.1:'dm',
                   1:'m',
                   1000:'km',
                   # time
                   8.6400e4:'day',
                   3.1536e7:'yr',
                   3.1536e10:'ka',
                   3.1536e13:'Ma',
                   #Pressure
                   1e9: 'GPa',
                   1e6: 'MPa',
                   }
    return scale2unit[scale]