Q re: L&R (Lat / Vert) DC Thresh on a Fairchild 670

What are they?
 
Last year I got the Vintage Compressor bundle from IK Multimedia and am really liking them. I am near the end of my 1st project with them and put the Vintage Tube Compressor/Limiter model 670 on my mix bus.
 
All is well and sounding great. Then last night, I found the pdf manual for these processors and discovered the L&R DC Threshhold controls. I had honestly thought they were little rivets on the processor emulation :)
 
The pdf states: exactly like on the original unit, set it fully counterclockwise for maximum softness of the compression knee; Set it fully clockwise for maximum hardness of the compression knee.
 
I brought up the project and, yes, they move and have labels. But I couldn't tell which way they are even pointing! I'm sure in the light of day today, I may figure this out more clearly.
 
I searched the vids on youtube and Groove 3 and, though the 670 is well covered, I did not find anyone using the controls or even mentioning them. I'm sure they are not something that will be hugely evident to the ear.
 
Does anyone use them? I will attempt to set them to a soft compression for this song if I can but I thought the knee was somewhat built into the large input gains and threshold knobs.

Well these have got to be the smallest controls in plugin history...Smaller than my actual mouse pointer! Thank goodness I had cataract surgery in January or I never would have seen them :)
 
Just for the hey of it, I flipped through the presets and there is (best if you have a magnifying glass) a pointer on these and different presets give different positions. They move independently of each other even when locked and there is no calibration so if you move one, getting the same position on the pother is a matter of luck IMO.
 
Anyhow, I dialed in a position somewhere between all the way left and all the way right and possibly somewhat towards the left, and I'm calling that quits :)
 
Nevertheless, I really am enjoying these vintage compressors for the sound and dynamic characteristics they are imparting to the song. Yehhh!