The Transformed Standard score is a weighted grade based on the mean and the standart deviation of the grade distribution. In this course, a modified version is used:

T_score = 100 - (TopGrade - Grade)/StdDeviation * 15

It highlights where a student stands in relation to his/her classmates and shifts the raw grade into the catalog range [0-100]. 70-100 range covers 2*StdDeviation.