Online advertising allows advertisers to precisely measure the impact of their ad spending. There are several types of online ads such as display, video, and social media ads. Publishers can generate ad revenue through broad ad networks that pay lower CPMs, targeted networks and agencies with higher CPMs and more control, or direct sales that offer the highest CPMs but require the most work. The amount of revenue depends greatly on the amount of traffic - an example site with 100,000 monthly unique visitors could earn between $6,000 and $60,000 per year depending on the type of ads used.