Anyone open up a speedometer?

I've opened up and cleaned up the tach so no problem there. The question I have about the speedometer concerns the trip meter reset knob. How do you get it out? Anyone try this successfully before? I just want to clean it up, not destroy it!
Thanks folks.

a bunch of times, but they are not all the same.

Good point. I should have been more specific. This one is on a 1980 shaft drive with the reset knob on the lower left side of the unit.