Wind

I read Ian99 as saying that a decent anemometer will measure speed not force. As such, it would be equally accurate anywhere.

Of course, it depends on how you define 'decent'. I'd have thought that a good rotating turbine-style of anemometer would have such minimal bearing drag that the turbine would always effectively spin at a rate proportional to the windspeed, regardless of the air density, i.e. it will be accurate everywhere.

An instrument that depends on the pressure force exerted by the fluid - e.g. a vane with a pointer that moves against a spring or gravity, will depend on density and therefore be less accurate. That said, anybody who's used an anemometer will know that the fluctuations are usually so great, gust to lull, that such inaccuracy would be hardly noticeable and thus irrelevant, or so I'd have thought...

thanks for that it has cleared some of it up.

So an anamometer built in the uk set to measure wind on a summers day at sea level in the uk is not accurate anywear else.

And yes i agree the beaufort is what on what you can see not a measurement.

One  example i have heard is that an aeroplane that takes off in dubai mid summer must have a higher take off speed to get the lift than it must in the uk where the air is denser.

So for colder denser wind do we get more power per knot of wind than in a hot country with lower density.