The Productivity Display is an indicator that appears inside production and generator buildings. It shows a value between 0% and 100%, based on how often the building is operating compared to its current maximum production speed.
Indications of power usage
For generator buildings, a lower efficiency means that less power is being demanded by the power grid. Due to this, generators will consume fuel at a slower rate based on efficiency. For example, if a coal generator is burning coal at 5.4 seconds per coal ore, but is at 50% efficiency, the actual burn time will be 10.8 seconds.
For production buildings, the efficiency is an indicator of average power use, as buildings will alternate between being on (using full power), and being off (using no power).