Gnd indicator does not point at gnd

[Dave42]

Hello,
The GND indicator does not point at grounded waveform when I ground the input (set S1 to GND).
Is there a way to reset the indicator?
Any help would be greatly appreciated
Thank you

[jye1]

Please try VPOS alignment by holding down VPOS button for 3 seconds while couple switch is set to GND.

[Dave42]

Thanks that worked