When a course has more than one instructor grading student work, even a well-written rubric will be interpreted slightly differently by each person — one grader might read "adequate evidence" more generously than another. Left unchecked, that drift becomes a fairness problem for students who happen to land with a stricter grader.

Calibration sessions fix this before it becomes visible to students: instructors independently grade the same handful of sample submissions, then compare scores and discuss any large gaps until their interpretation of the rubric converges.

Running a short calibration pass before each major assignment, rather than only once at the start of a term, keeps standards aligned even as instructors' individual habits naturally drift over the following weeks.