Difference in intensity from the blackbody radiation for μ distortion defined by the equation with n(ν) = 1/(e^{hν/k_BT_μ + μ} − 1). T_μ is the temperature to which the spectrum relaxes for an initial energy addition/loss of ΔE/E with ΔT_μ/T = 0.64ΔE/E =  ± 2.5 × 10^-9. ΔE/E =  ± 4 × 10^-9 is the energy addition/loss that gives rise to SZ distortion of 10^-9. The dimensionless chemical potential μ is given by μ = 2.2ΔT/T =  ± 5.6 × 10^-9.