Regarding the second page of this document, in the first example it calculates the DC CMR due to line imbalance Rs and an explanation is given in the first paragraph below (ignore the second example):
I don’t understand where the numbers 0.9990 and 0.0009990 come from.
I redrew the circuit model to simplify it and named the nodes as follows:
Can’t we show the path taken by the differential current flow direction using the nodes order such as a, b, c, d, e and the common mode currents direction as a, b, c, m, k and e, d, c, m, k?
If true, the differential voltage gain and common mode voltage gain seems not as given in the document. For instance, the differential gain to me seems like 20Meg/(20Meg+10k) but the document shows it as 0.999. I'm confused about how to calculate both differential and common mode gains mathematically here. How should they be calculated separately to find the CMR?