This is the code which is not working as expected, the Y value is wildly wrong.

calibration.py

import smbus
import time
bus = smbus.SMBus(1)
address = 0x48

print("Please ensure that the joystick is centred, the test will start in...")
for i in range(3,0,-1):
    print(i)
    time.sleep(1)
print("The resting value for each axis is as follows...")
time.sleep(1)
y = bus.read_byte_data(address, 1)
x = bus.read_byte_data(address, 0)
print("Y = ",y,"X = ",x)
print("Move the joystick to the top and hold...")
time.sleep(3)
y = bus.read_byte_data(address, 1)
print(y)