FIGURE 6.

(A) SNR is inversely proportional to step length ΔL. Simulated step detection threshold contours (SNR = 4) as a function of F_C, for step lengths ΔL = 0.3–6 nm at different stepping rates: k_cat = 10 s⁻¹ (triangles), k_cat = 100 s⁻¹ (squares), and k_cat = 1000 s⁻¹ (circles). Solid lines indicate step detection thresholds calculated from the exact formula, Eq. 10, and dashed lines indicate the SNR threshold calculated from the approximate formula, Eq. 25. L = 1000 nm, L_p = 50 nm, and d = 1000 nm. (B) Measured step lengths are attenuated by the nondimensional extension of the WLC. Step attenuation (ratio of measured to true step length) as a function of F_C, for persistence lengths of L_p = 50 nm (squares) and L_p = 1 nm (triangles). The measured step length was determined from the spatial frequency of a peak in the FTPWD. Lines indicate theoretical prediction, Eq. 9.