[Fzang]

I am well aware of the R/S system. In my application, if I choose to apply R/S wherever possible, it will apply non-capitalized r/s to some carbons as well. How does r/s work? Can't seem to find any logical explanation.

[Dan]

r/s Applies to pseudoasymmetric centres - these are cases where two of the four different substituents vary only in stereochemical configuration. Another example would be xylitol.

In short, r/s is assigned in the same manner as R/S, giving the R substituent higher priority than the (otherwise identical) S substituent. Note that pseudoasymmetric centres are invariant on reflection (unlike asymmetric centres).

In your example compound, RrS becomes SrR on reflection (and not SsR). RrS = SrR, the compound is meso.

IUPAC link:
http://www.chem.qmul.ac.uk/iupac/stereo/NQ.html#30

[Fzang]

Thanks. That makes fine sense