How to evaluate SAR data?

I know how to collect and make use of the data gathered by the sar tool, but I don't know how to interpret it correctly. For example, PAGING: I can see that my pgpin is 300.000 but how can I tell if that is good or bad, and what is the maximum _possible_ value of pgpin (not max(pgin))? Same with other values, IO: BREAD 1 million ... but what is the upper limit? If someone could hint me in the right direction that would be great. Thanks