Nevertheless, many web advertising companies require ads be placed above the fold. Marketing research done by Google shows that the viewability of adverts is affected by its position in relation to the fold as there is a significant drop-off below the fold. Each company tends to use their own definition of the fold. The BlogHer advertising network, for example, defines the fold as the top 768 pixels of the page. The FoodieBlogRoll advertising network defines the fold as the top 1000 pixels.