In this talk, I will illustrate some aspects of tracking in a particle physics experiment using the example of Bs0 --> Ds-+ K+- pi+ pi- decays, illustrating the importance of excellent tracking and momentum resolution for this kind of precision measurement. This 2020 measurement of the B0s decays using the full LHCb run 1 and 2 data sets yielded a world-best measurement of the B0s oscillation frequency Delta(ms) (at the time), and a measurement of the CKM angle gamma. Towards the end of the talk, I will spend some time on fast parametrisations I use for studies for LHCb Upgrade 2 using multidimensional Chebyshev fits which are linear in fit parameters, a powerful and fast technique that is applicable and useful throughout particle physics (and indeed beyond).