Hi Nizar,
Be careful with this NanoVNA accuracy sheet. It remains indicative, and as you say, accuracy remains dependent from hardware bridge and calibration load. The initial purpose of this picture here is to show that depending circumstances, it is sometimes relevant to choose another measurement method, than the common s11 one.
In the context of this topic (s11 measurement), you can't totally rely on these relative error measurement values. But for example if you get an X=1000 ohms value or higher, you are sure not to be in a confident frequency range, for capacitor or inductance measurement. Here, we have to consider this graph (configuration 1), as an helper here, no more.
73 - Jean-Roger
