Yes Martin that's right, I guess that's exactly want's him to figure out @Digitalvillage, in backlinking you need to mix the high PR and low PR, for the links to look natural.
Well, as such there is nothing called low level or high level of links. Its just good, average or poor quality links. Good quality links are those which are coming from reputed relevant websites. Average quality links are those which comes from relevant but less reputed website. Poor quality links are those which comes from irrelevant and less reputed websites.
low level BL = they have no value in SE because of many reasons like spammed to death, too much spam links in posts, copyright content etc... high level.. = unique and quality content, have page rank, low OBL hope this will help you.