RMN of the fitted perturbed attitude with respect to the error-free astrometric attitude versus the time interval between knots in the B-spline fit. The horizontal axis ranges from 1 to 30 s and the vertical axis ranges from 10 to 400 μas. The red line indicates the trend for short knot intervals (statistical noise, σ_Δψ,stat ∝ τ^−1/2), while the blue line indicates the trend for large knot intervals (fitting noise, σ_Δψ,fit ∝ τ^{1.890 ± 0.001}). The value of the exponent is constant withing the knot intervals studied in this work. The black line is the combined noise (σ_Δψ). The minimum noise is σ_Δψ = 17 μas at τ = 4.2 s. The noise at τ = 15 s is σ_Δψ,stat = 89 μas.