Some interesting reading there. Certainly implementing the simplified Hargreaves-Samani seems like it would be fairly trivial and I’ll tackle that tonight.
Silly question, but ET only deals with watering adjustments based on evaporation right (ie it will always vary a base watering amount upwards)? Is there a defined standard method for varying it downwards based on precipitation levels or is it just a matter of saying Xmm of rain means cut watering time by Y%?