Hey Jens,
great that the binding works fine for you. I’ve developed and testet this with openhab 4.x so im a little surprised, that it works with openhab 3 too.
The binding delivers the value as quantity of type temperature (see Units Of Measurement | openHAB) so the framework is able to convert this to your unit. Have a try to specify a state description on the binding as mentioned for example here:
for example i’ve two metadata entries:
state-format
%.2f °C
unit
*C
Have a try.
BR Sönke