Absolute values of the diffusion velocities from diffusion (lines) and those published by Thoul et al. (1994). All results are plotted in units of R _☉/τ _θ, where τ _θ = 6 × 10 ¹³ yr is the characteristic diffusion timescale for the Sun (Thoul et al. 1994). The dark solid and dashed lines are the diffusion results for H and O. The filled green circles show the results of Thoul et al. (1994) for H, O, and Fe (Z = 21). The diffusion results for helium are shown as the dashed red line. The diffusion results for Fe include one for Z = 21 (dotted blue line) and one for ionization states determined by ionization (the dot-dashed blue line).