Subtract from IAS or TAS...
Tooling around in the sky recently, I was trying to calculate the wind. Happens sometimes...
Anyway, I usually get the a/c generally pointed into wind and took the Ground Speed from the IAS. The thought occurred to me though that perhaps I should be taking it away from the TAS... (not a huge issue at the levels I'm at, but that's not the point)
I've come up with a number of reasons to do each, so basically I haven't come to a rock solid answer (but I'm leaning heavily towards TAS)/
Comments/answers anyone?
Cheers,
Turbofan