Front light focus questions

Hi all!
I have some questions on comprehending the clear front fixtures (Ch.101 thru 104) information in the conventional focus chart. 

1. What is the meaning of 12L @ 0? Is it the hot spot of the beam or the nearest edge be focused at SL 12' ?


2. Wrote in the red colored text:  DS cut @ +1. Is it to cut the bottom shutter at +1?
3. I have no idea what does “Cover 10L/R” means.

Since I'm from a non-English language region, it's quite difficult for me to understand some terms and methods that are different from what we normally use.

Thanks,
Adrian

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