So, I'm trying to prove [tex] \Delta\nu\Delta\tau\approx0.44 [/tex] where; [tex] \Delta\nu [/tex] is the FWHM in freq domain for a gaussian pulse and [tex] \Delta\tau [/tex] is FWHM in time domain for a gaussian pulse. I do the problem by taking a standard gaussian exponential and finding the FWHM in both the time and frequency domain. BUT, my answer is always EXACTLY a factor of 2 off. Ie. I get [tex] \approx0.88 [/tex]. No matter what form of a gaussian I use it is a factor of 2 off. 0.44 is the right answer (its quoted in many books). Anyone familiar with this derivation?