Understanding the Occupancy under PIX 2303.30

Question

I am profiling my renderer to do some optimization. To help me I use PIX 2303.30 and I successfully get captures. I have theses questions about the occupancy:

1. What is really the occupancy, why does it ranges from 0 to 10?
2. It looks like the VS and PS shader occupancies are added together. Why?
3. Why does it stops in the middle on a timelapse?(See pink line)

Thanks for helping!