TOA uncertainty obtained from various noise-added profiles as a function of the simulated S/N. Top left panel: results for a simple Gaussian profile. Top right panel: results for a Gaussian profile with a notch. Bottom panels: results for the analytic templates of PSRs J0218+4232, J1713+0747, and J2145−0750, respectively, as derived from NRT data. CCAs are shown with different colours and markers, as indicated in the legend. The solid black line in each panel is a fit to high-S/N (> 10) FDM data and is extended to low-S/N data. At each S/N we plot, ten simulations were run, although they are typically indistinguishable at high S/N. The inset within each panel shows the profile. (a) Simple Gaussian profile. (b) Gaussian profile with a narrow notch. (c) PSR J0218+4232. (d) PSR J1713+0747. (e) PSR J2145−0750.