Hi Andy,
Netro does not need rain sensor and you might want to check the Netro Whisperer sensor which monitors real-time environmental conditions.https://www.netrohome.com/en/shop/products/whisperer
To correct rainfall, please go to Discover page, tap the "+" button on the upper right corner and select "Correct Rainfall". If the current weather provider is not accutate, you can switch to other weather channels through Settings->Weather Provider.
Thanks,
Netro Support