Hi all, reading an article I've encountered the concept of power at the fundamental frequency, google didn't help me. Could you please give to me any hint about this problem? It is at least one week I'm dealing to understand what the "fundamental power" is!!! there is a kind of wave, express as: Y(t)=a1*sin(omega*t)+b1*cos(omega*t)+a2*sin(2*omega*t)+b2*cos(2*omega*t)+a3*sin(3*omega*t)+b3*cos(3*omega*t) they say that fundamental power is: a1^2+b1^2 and the square error of the fundamental power is sqrt(2(SE(a1)^4 + SE(b1)^4)) to me it seems quite strange! The power of wave is the work/time, but I guess that the fundamental power it not related to the work/time meaning. And anyway, how it can be approximated to the squared amplitudes??? also how the square error of fundamental power becomes the dirty thing I wrote above!! thanks a lot, Mauro P.S the article is: Methods for Diagnosis and Treatment. of Stimulus-Correlated Motion in Generic Brain Activation Studies Using fMRI. www-bmu.psychiatry.cam.ac.uk/sitewide/publications/journal/bullmore99met.pdf and the formula I'm talking about is at the beginning of page 42.