Hey Kalle,
Just got round to implementing this. It's working!
Was just wondering how accurate you think it is? Have you tested it using a thermometer?
-P
I think it is reasonably accurate when the thermometer is outside the box, but as Kalle says it will be off by a constant value so you will need to offset by always adding 'x' degrees. In other words, it needs to be calibrated. Hopefully it will always be off by exactly 'x' degrees. In my testing it seems to be pretty good.
It's easy to add or subtract using a single python action.
Lets assume you've got the temp from HALX but it is too low by 7 degrees. You can use
PY.ExecString result = {LastResult} + 7
now {LastResult} will be 7 greater than it was.
Note: you'll need to enable the python plugin (PY) for this to work.