Reading 23 waterfall chart on p. 215

I’m having trouble understanding how to interpret Exhibit 23: Manager Allocation by Active Risk Level. Looking at the upper left corner, I get that with 100% investment in the index, tracking risk is zero. Also, the right edge: 100% in Active C produces 8% tracking risk. How do I interpret other areas of this chart?

OK I get it now. Vertical lines give the portfolio allocation; the x-axis gives portfolio tracking risk.