The relaxation values of the set R'(*θ*) include the spin-lattice, spin-spin, and cross-relaxation rates at all field strengths.
These rates are respectively (Abragam, 1961)

where *J*(*ω*) is the power spectral density function and *R*_{ex} is the relaxation due to chemical exchange.
The dipolar and CSA constants are defined in SI units as

where *μ*_{0} is the permeability of free space,
*γ*_{H} and
*γ*_{X} are the gyromagnetic ratios of the *H* and *X* spins respectively, is Plank's constant divided by 2*π*, *r* is the bond length, and
*Δσ* is the chemical shift anisotropy measured in ppm.
The cross-relaxation rate
*σ*_{NOE} is related to the steady state NOE by the equation

The relax user manual (PDF), created 2020-08-26.