Example of the epoch-folding in P–Ṗ-space for NuSTAR observation 2017F. The χ² value at each P–Ṗ pair is color-coded. The graphs at the top and on the right show the cut along the respective dimension for the most significant measurement at P = 415.7050 ms and Ṗ = 6.5 × 10⁻¹¹s s⁻¹. The orange dashed line shows the 99.99% significance line taking the number of trial periods into account.