Barometer calibration 'offset'

[skyewright]

I realise Boris is busy, but if there is time sometime:

In addition to (rather than instead of) the current barometer options would it be possible to allow for a calibration offset?

If used in addition to the existing calculated options, I'm guessing that the new offset would be applied before performing the calculation.

Reason: With RFXCOM and WMR928 sensors the pressure is coming from the sensor, so it is a raw value. My sensor seems to read low (I'm querying if this is a fault[1]).

On the console this isn't much of a problem because setting the \"sea level\" value is just a matter of clicking till it gives the value you want, but without a way of plugging in an offset I can't get meteohub to give me a sensible figure at all.

[1] Just spoke to a technician and he says it may just be a temporary problem as the pressure sensor can take up to 2 weeks to setle down! However, it would still be nice to be able to put in a 'calibration' offset.