Small Engines (Lawn Mowers, etc.): craftsnan elec chainsaw

Question
I have an electric craftsman chainsaw, model 31534160. There is a black knob on top, next to oiler pump knob. Black knob can be turned, screwed up/down, but, what does it do? There is also a tiny pin between that knob and saw housing.

Answer
It was used as an auto chain sharpener but was not very effective which is why no chainsaws today have this feature.  If it worked then all saws would have this feature.  I believe McCulloch offered auto sharpening on a few saws about that time period.

Eric