In fact EAS is regarding to the "clumping up" of air molecules at speed. Try to imagine a pitot tube where at low speeds the molecules are free to exit the tube without being clumped up. As the a/c speeds up more and more molecules try to enter a rather small hole (don't you dare pprune, this is a sacred place
). This clumping up in the pitot tube, which very roughly speaking is an instrument that senses pressure or number of molecules over time, makes the ASI overread. EAS is therefor a calibration from CAS. IAS can be more, less or the same as CAS. CAS is always more than EAS. EAS is always less than TAS, and TAS can be more, less or the same as GS.