The underlying structure of the phrase is:
1. X can be measured against Y.
When you measure e.g. a piece of material with a tape measure, you place the tape measure against (i.e. next to) the material.
The same applies in metaphors of measurement, as in your example.
("Benchmark" is a surveyor's term, with a quite complicated definition. But in popular usage, it tends to mean "something that serves as a measure".)
Student or Learner