US Patent 10210541 Crediting impressions to advertisements in scrollable advertisement units

An online system presents a scrollable advertisement unit including multiple advertisements to a user. The scrollable advertisement unit presents one or more advertisements in a display area, and allows a user to navigate through the advertisements in the scrollable advertisement unit to display different advertisements in the display area. One or more rules for crediting an impression to an advertisement in the display area are applied, and a tracking mechanism associated with the advertisement in the display area is loaded if at least one rule is specified. Loading the tracking mechanism identifies an impression of its associated advertisement.