Line 1 in panel (a) is vertical profiles of bΔθ^ from Fig. 1(e) with σ¯s being 17.13 μrad, line 2 in panel (c) means horizontal profiles of bσ^s2 in PMMA where Δθ¯ is −6.18 μrad. They are all drawn as discrete points in panels (b) and (d), and solid lines represent the theoretical biases derived from Eq. (8).