Using Android App version 2.4.43 with OpenSprinkler firmware 2.2.0 (3).
The location is set to Israel and on every app start, the weather temparture is in fahrenheit.
Going into Edit Options->System and enabling “Use Metric” and click Submit, the temperature is changed to celsius as it should. However, on the next time the app is started the temprature is in fahrenheit again and the “Use Metric” toggle is disabled again.