The crucible reviewer's progress percentage calculating rule

[redlin6688]

Is anybody knows the exact calculating rule of The crucible reviewer's progress percentage .

I have the infomation from  Using Progress Tracking ,which indicating that:

  "progress tracking also takes lines of code and revisions into account."

but I am confused about this, and found that it is not as expected in project reviewing practice.

As I receive a review activity which contains 2 files to be reviewed,

          file1: new added file, only 3 lines

          files2:  has 35 lines in the latest revision, and 34 lines in last revision.

After I review the review invitation, I start the reviewing, and I click the file1,and review it and set to read state, 

then I go the details of this review activity, and find that my review progress percentage is 37% .

So how does this come from, the real calculating rule is what?