Hi, I'm a little bit confused as to how I can calculate the amplitudes of the first, second, third, etc harmonics of a waveform, following FFT. Due to file size issues, Ive attached the excel file here: http: //www.2shared.com/file/uPYkxFK1/FFT_excel.html The waveform is that of blood going through the heart (in Litres/Min). This data has been obtained at 50Hz (50 times a second), and there are 4096 data points. However, i'm having a little trouble in determining what the first harmonic is. Would this be the point at which the amplitude is the highest? In that case it would be "0.524902344" and that would make the 2nd harmonic "2 x 0.524902344" = "1.049804688"? Would this mean that the corresponding amplitude would essentially give me the 'amplitude of the first harmonic" etc. Or am I completely wrong? Secondly, is there any other way (quick or slow) of determining the first, second, third, fourth,... harmonics (and their amplitudes) in excel? Lastly, I need to calculate the "amplitude of mean flow", but I'm not exactly sure what this means and how one would be able to do this. Any help will be greatly appreciated. Thankyou!!