Two rules at once is the difficulty layer, and on the APM it is most of Set II. Carpenter, Just and Shell found that what separates the strongest solvers is not knowing more rules but managing several at once: finding which element belongs to which rule, holding the found rules while looking for the next, and checking the candidate against all of them. This drill serves only items the bank marks with three or more rule instances.
What you see: a grid where one rule almost works. What you do: keep it, and find the next.