slow time scale การใช้

The idea is not the the fast and slow time scales are truly independent / decoupled, just " mostly " independent, and that's often good enough.
The precision with which the field of celestial mechanics is able to describe the movements of bodies of the solar system is due to the incredibly slow time scale of astronomical, evolutionary change.
The passage to analysis of autonomous dynamical model of Costas loop ( in place of the non-autonomous one ) allows one to overcome the difficulties, related with modeling Costas loop in time domain where one has to simultaneously observe very fast time scale of the input signals and slow time scale of signal's phase.