Link counts are not additive. In the PageRank formula a page divides its vote among its outbound links, so a page with 300 external links passes a sliver of what a page with three passes. Sitewide footer or blogroll links are many links from one source, and footer links planted across many sites are named link spam. Link velocity, a boost for a rising link count and a penalty for a falling one, is unconfirmed; a sudden surge of bought links is what SpamBrain is built to catch.