Does "the curve" qualify for your meaning?

Marking "on the curve" is taking the grades, listing them in numerical order, then superimposing that list on a normal distribution curve, so that (for example) the top 5% get an A, next 12% get a B, middle 66% get a C, lower 12% get a D, bottom 5% fail (E or F or whatever your system uses). The ranges may be adjustable to suit individual preference.

This gives the counterintuitive possibility of having papers with 37% right, for example, getting a B or a C instead of failing...