Reproduction of the effects of AL and AC source motion in the PSF model. The upper two panels show two model PSFs that are identical apart from the configured AL and AC source motion: in both cases τ̇ - τ̇₀ = −0.045 pix s⁻¹ while μ̇ - μ̇₀ = −0.975 (left) and 0.975 (right) pix s⁻¹. The lower left panel shows the difference between the two, which is dominated by the reversed sign of the shearing effect due to the change in sign of the AC rate. The lower right panel depicts the equivalent effect seen directly in the data, and is produced by stacking many observations at μ̇ − μ̇₀ > 0.975 and μ̇ - μ̇₀ < -0.975 pix s⁻¹ and plotting the difference.