Very confusing labeling

Hi, I have a GE dual-element electric water heater that is no longer heating water. After turning off the power, I removed the access panels to check the resistance of the heating elements. One reads about 10 ohms and the other is open. I'm going to replace both, but I also want to ensure that it's wired correctly. The manual (which covers a range of exact models) contains a table for wire size and breaker amperage based on watts. But I find the label on the heater confusing: Volts 240/208 Wattage: Upper 4500/3800 Lower 4500/3800 Total 4500/3800 <---- huh? How can the unit have two 4500 watt elements and have a total wattage of 4500 watts? What am I missing?