How to interpret Negative KR?

So, first off, I know it's not bad, but how is the relationship of (-)KR and spark advance? I know (-)KR adds timing, but temporally how does it work? I see timing stagnate while KR still drops or vice versa, so I assumed it's not instantaneous.

If anyone could explain how and if KR directly and/or indirectly alters spark advance, I would greatly appreciate it.

The picture is positioned at a point in the log where I'm getting 30.3 degrees with -8.5 KR. That's only 30.3 correct? What does the -8.5 KR use as a reference?

Thanks, and sorry if this is posted in the wrong place.

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