Here we are again. Same old argument. See the foto.

If your car has one of these then you can alter the timing to enable you to run with the Octane you like. These " octane adjusters" were installed in International versions of some MB M103 models. These were provided for cars that would possibly end up in a third world country which could only supply very poor octane fuel. If you have a car with one of these then the owners manual would have a section explaining the required adjustments re fuel octane.

Cars destined for most western countries with more strict emissions requirements came with a set resistor that would set the timing to a constant. In your owners manual there would be a section specifying the octane fuel to be used. there would also be a disclaimer that would say that using a lesser octane fuel than specified would risk the integrity of the engine.

Search R16 adjustments in this forum. II will also include a foto of the R16 resistor in a W124.