Bill Slawski tells us about a Google patent granted last week that explains how a crawler decides whether it should re-index a Web page after finding a small change in the content. The patent also describes how Google might check for changes on a page, comparing a newer version with an older one. Slawski describes the focus of the patent, what makes sense, and why a patent like this one might become important to ecommerce stores that want to display links to specials or featured content on pages.