BARB collects device-based data whenever anyone in the UK watches a broadcaster video-on-demand (BVOD) service on PCs, tablets and smartphones. These data provide granular evidence of how online TV is being watched. How do we do this? Together with Kantar Media, we work with broadcasters to embed software code into their BVOD services across different online platforms; this process is known as tagging. The tagging implementation is independently audited by ABC to ensure the data meet our standards. BVOD services on 40 different online platforms have now been tagged and passed the audit. Whenever someone in the UK watches a programme through a tagged BVOD service, be it live streamed or on-demand, the embedded software code generates online TV viewing data detailing what has been watched, and, to the second, for how long. These census-level data tell us the number of PCs, tablets and smartphones that are being used to watch programmes, both on-demand and live streamed. Importantly, these are not people-based figures; they represent the total number of devices that are being used to watch participating BVOD services. Device-based data cannot tell us the number of people watching or who they are. This kind of insight is critical to our customers as they plan for viewers to see the content that they make. For this, we need the BARB panel. The Dovetail Fusion process combines these device-based data with our panel data in order to deliver multiple-screen viewing figures.