请教一阅读难句

Thus，for instance，it may come as a shock to mathematicians to learn that the Schrodinger equation for the hydrogen atom is not a literally correct description of this atom，but only an approximation to a somewhat more correct equation taking account of spin，magnetic dipole，and relativistic effects；and that this corrected　equation is itself only an imperfect approximation to an infinite set of　quantum field-theoretical equations.

我的问题在三个红色标注的部分：最后的this corrected equation是指代Schrodinger equation呢，还是指代more correct equation。请高手赐教~

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Fresh calf, not veteran.

The structure author intend to trap flow is below:

There are 3 studying subjects on hand. In which, " S equation" was imperfect for subject 1 but the "S equation" seemingly matched the subject 2. Then " more correct equation" was elicited, meanwhile author poured so many words to describe subject2 scale. At lase, author contiued to point out the imperfect of " M equation" really limited its subject3.

Logic structure:    

Subject 1          S equation    

Subject 2          M equation    S

Subject 3          T equation    M

                                 T....

Looooooook forward to participants.