nvidia-settings overclocking; How do you know the offset to use?

To overclock/underclock nvidia card I see this:

The example GPUGraphicsClockOffset[3] didn't work for me, another howto showed the same command but with offset GPUGraphicsClockOffset[1]. That didn't work either, so I tried GPUGraphicsClockOffset[2], then GPUGraphicsClockOffset[4] which finally worked.

Where is it described which offset to use?

This is what worked for me: