Nokia 5110 contrast

[SYWindveer]

I have three 5110 LCD displays, of which two were not working on my tinypilot.
I appears the contrast settings vary wildly between them.
On Arduino I can adjust the Vop untill they are readable

In home/pi/.pypilot/lcdclient.conf I see a contrast setting:
 
class LCDClient():
    def __init__(self):
        self.config = {}
        self.configfilename = os.getenv('HOME') + '/.pypilot/lcd.conf'
        self.config['contrast'] = 60

Is this the line I should change to adjust the contrast ?