Wenxi, i hope you don't get flamed for this because i recall this has been ask many times. a search using the function above will tell.
Just turn the knob to between 12 - 2pm, and let it settle and see what you get. From there adjust accordingly. I suppose when you started this thread, you already know what's the RH you need to achieve?
Anyway, i'm 4 days late, but here's wishing you a belated happy birthday. =)