The "eta_scale" in CR72.The "eta_scale" in CR72.Dear Edward. I was inspecting the code of model CR72. http://svn.gna.org/viewcvs/*checkout*/relax/trunk/lib/dispersion/cr72.py?revision=HEAD This is calculated as: eta_scale = 2.0**(-3.0/2.0) = 0.35 which is: 1 / sqrt(2**3). This differs from the definition in: http://wiki.nmr-relax.com/CR72_full#Equation http://www.nmr-relax.com/manual/full_CR72_2_site_CPMG_model.html http://www.nmr-relax.com/api/3.1/lib.dispersion.cr72-module.html where: eta_scale = 2.0**(2/3) = 1.58 which is {3}sqrt(2**2). If I compare to: http://wiki.nmr-relax.com/B14#Equation_compared_to_Carver_Richards_72 (DOI: 10.1016/j.jmr.2014.02.023 , eq 70,) And to, (DOI: 10.1016/S0076-6879(01)39315-1 , eq 25, with the twist that "tcp_Pa is the delay between 180 pulses in the CPMG pulse train", "delay/180/delay/delay/180/delay " so that tcp_Pa = 2xdelay Then really the manual should use: eta_scale = 2.0**(-3/2) or 1 / 2 sqrt(2)