1.Take a knob cap and verify if it is broken or has flaws around; pick out unqualified ones
2.Adjust the two knobs in counterclockwise till they reach the ends and install the caps, as illustrated on Picture 1
3、Make sure the calibrations on the caps indicate down vertically,install them to the ECHO and VOL knobs on front mirror, as illustrated on Picture 2
CALIBRATION DOWN VERTICALLY