Difference between time delays of repeating multiply imaged FRBs for increasing angular distances at the radial critical curve of the NFW profile of Sect. 2.3 when the virial mass of the NFW profile is increased by 10⁵ solar masses (solid line), by 10⁷ solar masses (dashed line), and by 10¹² solar masses (dash-dotted line). The measurement precision of τ_ij for one measurement, approximately 1 ms, is shown as a dotted line.