To be honest, I don’t think ‘% Watering% would make it obviously clear to a typical user what the parameter is for either. The matter of fact is that there are technical terms that are difficult to explain without at least one sentence of explanation. I understand that most users don’t read user manuals and don’t want to read user manuals. I agree that most products should be designed to be self-explanatory. But at least they should be aware there is a user manual they can refer to when something is not immediately clear.
As some personal experience: I regularly upgrade my cameras. A product like a camera has been designed and refined over so many years that I should think I don’t need to read a user manual any more. But there are still a lot of advanced features that I simple do not understand without reading the manual. Maybe if one day Apple designs a camera, or sprinkler controller, they can do it in such a way that you don’t need to read the user manual. Until then 🙂