[DML] rheostat?

[Deloreanernst@xxxx]

Hi... this is my first question now that we're real owners! :) We haven't 
gotten an owner's manual yet, so we're still trying to figure out what some 
of the buttons do. The little knob under the radio to the left, is the 
rheostat knob?? If so what does that do? Thanks a lot! :)
~Rick
VIN 11174