As hinted above, I already got an answer elsewhere. Nonetheless, I'd like to also keep it here for the record. Basically, the answer is already included in the original post, as it prints the individual variables into the "Log" window.
For the third-degree polynomial, I could have just used:
Fit.doFit(2, x, y); // 2 is 3rd Degree Polynomial
Fit.plot();
rename("Calibrating curve");
And then the can be extracted easily as thus:
a = Fit.p(0);
b = Fit.p(1);
c = Fit.p(2);
d = Fit.p(3);