It is the equivalence principle that provides the bridge between the ideal $SR$ model and the real world. According to it, we can find at each event a set of local inertial frames (LIFS), which may be small or large depending on
I.) Distribution of nearby masses
ii.) Accuracy we require
Rindler: Relativity, Special, General and Cosmological, page-36
What does Rindler mean here by the smallness or largeness of an inertial frame?