Hey there @dmulcahey, @Adminiuga, @puddly, @TheJulianJES, mind taking a look at this issue as it has been labeled with an integration (zha) you are listed as a code owner for? Thanks!

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It's limited per ZCL spec. Search for LocalTemperatureCalibration in the Zigbee Cluster Library document.
If other thermostats support more, they're doing it out of spec, so we can't know they do. We can manually add them to another ZHA entity class that allows a greater range (-7°C to 7°C): https://github.com/zigpy/zha/blob/17139586ee2ad2f81a11061b6fb9b889422b006e/zha/application/platforms/number/__init__.py#L857-L867

The class should be renamed then if it's not Sonoff specific anymore.

Just my 2 cents: with the new Quirks V2 API, I would expect that if a new thermostat device exposes a number entity named "local_temperature_calibration", that metadata overrides any zha thermostat matched config (like the ThermostatLocalTempCalibration).

Currently, when I add that metadata to a v2 quirk (https://github.com/zigpy/zha-device-handlers/pull/2808/files#diff-5ef71546921bf190205a1ab63763070f285bda5da453bf8c071abf5468ac3ed5), I see 2 number entities instead of 1, meaning the override doesn't happen. Or I am doing something wrong while testing?

What I believe it happens:

• ThermostatLocalTempCalibration gets attached as entity to any Thermostat device with unique id: "ieee-endpoint unique id-cluster id-local_temperature_calibration" (link)

• a quirk v2 number entity which wants to override that gets added with unique id: "ieee-endpoint unique id-local_temperature_calibration" link. It would not match with the one it would want to override, thus it results in 2 distinct entities. The fix would be to harmonize the way the unique id is computed in between those 2. Problem is this part which fails to overwrite entities.

Here is a patch that enables entities overwriting: zigpy/zha#328. This is a general solution.
A workaround until the we will have the general solution: zigpy/zha#329