Plumbing risers are often drawn as isometrics. They show each stack, each branch, pipe sizes and the fixtures connected at each floor.
A plumbing estimator uses them for pipe sizes and fittings that floor plans hide. A restroom group may show only as fixture symbols on the plan.
Take sizes and fitting counts from the riser. Take horizontal lengths from the plan. Take vertical lengths from the floor-to-floor heights.
Count the fixtures on each riser. Compare the count with the plan and the fixture schedule. They should all agree.