question about checking for errors using DVDINFO

i'm sorta clueless here. i've used dvdinfo to check for crc errors on all of my discs. sometimes it will say no errors but there will be several "bad spots" during playback. or it will give several errors and there may be only one or no errors on playback. i've also used the PI/PIF, jitter test but don't know exactly how to read the results. i found an explanation on another forum board but it was too technical for me to understand. can someone try to explain how to read the results for this kind of test? i'll try to post an image of one of my results if needed. thanx.