Leak down and compression numbers in PPI.
 

In terms of buying the car, what's the general ranges of acceptability regarding both test?

Please forgive my ignorance.

Generally you want compression numbers to be within 10% high to low. You want leakdown to be consistent but not beyond 7-9%, which is indicative of impending top end work.

I've seen many tests where the compression was decent but one cylinder showed a dramatic leakdown number. This is cause by dislodged carbon chunks getting trapped on the valve seat. Drive and re-test to be sure.