Hello, The program fitting_main_kex.py ( in the relax.tar.gz compressed file https://gna.org/task/?7712) contains a mistake I made in the function 2D num (the 5th one) in the script fitting_main_kex.py . line273: tcp=Tc/(nb_pulse) ==> tcp=Tc/(2*nb_pulse) and consequently: the line 274 can be removed and line329: t115 = N/2 ==> t115 = nb_pulse; Indeed nb_pulse is the vector which contains the number of 180°pulses of ONE cpmg block. I am sorry for that, Kind regards, Mathilde