Calibrating Wind Direction

[blue2]

I have a Maplin N96FY (Xmas Pressie) up and running well with Cumulus V1.9.2 build 1032. With very light winds now (0.1 m.p.h.) from the SW I've found that the wind direction is always 90* out, i.e on the screen it will be indicating from the SE but in reality the wind is blowing from the SW.The Cumulus display shows the wind direction is coming from the S to SSE which is more accurate than the screen display.
What correction figure do I enter in the Cumulus calibration page?

Nigel

[steve]

To answer your question, you want to add 90 to the bearing, so you put 90 in the wind direction offset box.

But I think you really need to investigate why it's apparently 90 degrees out. Did you orient it correctly when you installed it? Can you get someone to hold it pointing north, for example, and see what the console shows?

Note that Fine Offset wind vanes have a tendency to flap around, almost randomly, so the 'instantaneous' bearing you see on the console and in Cumulus can vary quite a lot. The average bearing calculated by Cumulus tends to smooth out the variations and give you something closer to the wind direction.

[peterh]

Witgh very light winds, you are bound to get readings all over the place.

But Steve's assessment seems correct: I think the wind vane might not be correctly oriented.

[blue2]

Thanks for your input gents. I added 90* to the wind direction offset box yesterday and the wind direction on the Cumulus screen is matching or in sync. with the wind vane and showing SW at 1.6 m.p.h but on screen its continually shows SE 0.0 m.p.h.
When I mounted the weather station I orientated it to true north adjusting the difference from magnetic north using the information from the latest OS map and info from the Met Office at RAF Shawbury and on-line.

At the moment Cumulus is showing wind at 2.2 m.p.h from 227* SW and the display screen is showing 0.7 m.p.h at SE and the wind vane is freely rotating pointing SW.