Tube of oil(?) in my humi

[Langod]

I was just gifted a nice used humi by a friend.
It has a small glass vial of oil included in a little wooden case. My friend said he thought it was to help stabilize temperature -- but I find it awfully small to have enough thermal reserve to maintain temperature in a decent size desktop humidor.
Is that what it's really for? Or something else?
You can see it in the picture below in the center above the lighter and cutter and below the big Gurkha cigar. It's in a wooden case labeled "humidor"
I can take a better picture of it tonight if you need more detail.