1995 w124 E280 estate HFM resistor position

[killingtime88]

Just a quick one, my E280 has a seven position plug on the nearside bulkhead just below the windscreen.I have done some reading up and have come to the conclusion that this is a preset for the HFM system that is used to adjust the ignition timing if low octane/poor quality fuel is used.However i cannot find any info on the correct position for it.Except that the higher the numbers are for lower quality fuel.It is currently set to number 3.
Any advice will be welcomed.
Regards Paul

 

[television]

This device does little or nothing and I would leave it in the middle, it is an advance and retire

 

[killingtime88]

Thanks Malcolm