"This is a fundamental flaw in Flarm, which surely could be much improved by
building in a wind algorithm to correct the indication nearer to heading.
All navigation programs have them."

As another poster mentioned, you really need a heading input to achieve this. Whilst PNA's use drift while circling amongst other methods to determine the wind, they require frequent & sustained 'circles' to achieve this - not so good for wave & ridge. LX quote 3 circles from memory and all the operating notes warn of the associated unreliability. An attempt to use an algorithm to achieve this in Flarm would result in large variations in accuracy. Sometimes the relative bearings provided would be correct and sometimes, they wouldn't. Though currently an imperfect system, at least it's consistent.

CJ