The ability to see the efficiency of a production building is great. I think it would be even more useful to detect the amount the items flowing through a conveyor belt. It would help us use belt capacity more effectively, replenish bus supply, and throubleshoot bottlenecks.
You would mouse over a belt and see sometime like "Conveyor Mk. 3: Iron Ingots - 240/270 max capacity per minute."
This abililty could be tied to a milestone or research. Ideally it should be available around the Mk.3 belt appearance because that belt has a capacity that does not match a multiple of 60 .
Perhaps as an alternative, the ability could be tied to a hand slot tool. It would give you something natural to carry around the factory instead of a weapon.
We have space elevators, holograms, and light-based construction technology. Please give us a conveyor throughput sensor! We efficiency sticklers need it!