This mastery based approach makes the most sense to me. The difference between grades and percentages is really weird. In some sense, we expect a 90% grade to m

This mastery based approach makes the most sense to me. The difference between grades and percentages is really weird. In some sense, we expect a 90% grade to mean you were able to solve problems on 90% of the material, or with a 10% error rate. However, in some of the higher level classes, the tests are not on whether you have learned and can apply the material, but whether you can solve new types of problems that you haven't seen before. I've always found these sort of tests to be quite bizarre, as you really can't study for them, and whether I would come up with the required insight in the time limit was an inconsistent indicator. They seem better suited as problem sets.