Phil,

Thinking about the 90 & 270 degree problem (or any 2 directions 180 degrees
apart), the correct average should be 0 degrees.
I know that 0 degrees = 360 degrees, but in this case, where the wind is
blowing from opposite directions there should be, on average, NO direction.
Imagine a helium balloon being blown for half a day in one direction, and
for the other half a day blown in the opposite direction at the same speed.
It will end up where it started. What is it's average direction for the day?

The same problem arises with 90,180, 270 & 360 degrees, if you're trying to
average 4 directions.

Henry

"Henry" wrote in message
...
Phil,

For 2 directions:-
Put your larger direction in A1.
Put your smaller direction in A2
In A3
=IF(A1-A2180,(A1+A2)/2 +180,(A1+A2)/2)
If there's more than 2 directions, it gets complicated.
For 4, 8, 16, 32, etc directions, I suggest you do repeated averaging.
Average1 = (average of Direction1 & Direction2)
Average2 = (average of Direction3 & Direction4)
Overall average = (average of Average1 & Average2)

With other numbers of directions, the maths is beyond me!

BTW, what's the correct average of 90 degrees and 270 degrees?
Is it 180 degrees or 360 degrees?

Henry

"Phil" wrote in message
ups.com...
Hi all,

One of my students, a meterologist, has asked me how to calculate
average wind direction over a period, and I am stumped. He has a column
of numbers, representing direction in degrees, and simply wants the
average direction for the column. However he is coming across what I
guess is a perennial problem, ie:

Wind Direction
355
5

where using =Average will give the result 180 - of course the real
average should be 360.

I've searched this group, and found an earlier post for a similar
problem, that suggested the formula:

=MOD(DEGREES(ATAN2(AVERAGE(COS(RADIANS(A2:A3))),AV ERAGE(SIN(RADIANS(A2:A3)))))+360,
360)

However this has only given the result 5

The recipient of this earlier post seemed happy - but I can't get it to
work!

Can anyone suggest an answer? The wind directions are simple numbers,
not formatted as degrees or anything, and it's only the average my
student is trying to obtain.

Just shows the teacher doesn't always know it all!