Since there are no real inertial systems in reality, when a weak gravity field appear, because only radial gravity fields exist and no homogenous fields, there only a quasi inertial system (QUIS) can be constructed in these fields. Real inertial systems are only constructable in fieldfree spaces, far from every material body and neglecting quantum gravity structures. If gravity fields appear, even weak ones like in example of Earth field, only QUIS are constructable. This QUIS allows only a limited description of physical measurements because it deals with radial field lines of gravity, which are supposed to have a range of Planck-length at the center of Earth resp, the material body. Then the smallest QUIS, which can be constructed on the surface of planet Earth has a range of ca. 10u207b¹u2075 m. Smaller metrical length statements on the surface of Earth are senseless. If the measurements have to be finer, one must go afar from surface of the planet, where the radial field lines have greater distance and in this case greater QUIS can be defined. Then physical behaviour of interactions then can be described without contradictions in smaller ranges.