Chi is the combination of Win% (as determined by efficiency numbers) and Acc (Accomplishments). In fact it's just the average.
Here are Alabama's accomplishments:
Alabama17 USC, 40 Western Kentucky, 24 Mississippi, 102 Kent State, 81 Kentucky, 58 Arkansas, 7 Tennessee, 11 Texas A&M, 28 LSU, 55 Mississippi State
They have racked up the most accomplishments so far, so they get a 1. Everyone else gets a score relative to this.
Penn State102 Kent State, 44 Temple, 61 Minnesota, 89 Maryland, 3 Ohio State, 119 Purdue., 21 Iowa, 60 Indiana
Acc: 0.65
Summary: decent win% (0.65) and decent accomplishments (they have a top 10 win)
Boise State93 Louisiana Lafayette, 15 Washington State, 105 Oregon State, 103 Utah State, 68 New Mexico, 69 Colorado State, 53 BYU, 114 San Jose State, 100 Hawaii
Acc: 0.44
Summary: good win% (0.84), but they greatly depend on the Washington State win
Tennessee42 Appalachian State, 16 Virginia Tech, 51 Ohio, 18 Florida, 22 Georgia, 81 Kentucky
Acc: 0.66
Summary: decent win% (61), a few solid top 25 wins
Wisconsin28 LSU, 85 Akron, 116 Georgia State, 88 Michigan State, 21 Iowa, 37 Nebraska, 45 Northwestern, 122 Illinois
Acc: 0.43
Summary: good win% (80), wins were better a couple of weeks ago
Auburn70 Arkansas State, 28 LSU, 104 Louisiana Monroe, 55 Mississippi State, 58 Arkansas, 24 Mississippi, 83 Vanderbilt
Acc: 0.40
Summary: good win% (79), wins are starting to slide
Pittsburgh5 Penn State, 106 Marshall., 35 Georgia Tech, 86 Virginia, 4 Clemson
Acc: 0.70
Summary: average win% (48), but great wins (2 top 10 wins)
Here is the top 25 teams just on accomplishment
and here is the top 25 teams just on win%