To make the engagement reports more accurate, it is recommended to unify visitors that are using multiple devices and/or browsers into one visitor.
Note that this feature requires a unique ID provided on the client side. In most cases, this feature is available on websites that have a log in feature.
window._rd_queue = window._rd_queue || ;
window._rd_queue.push(['unify', VISITOR_ID, VISITOR_NAME]);
VISITOR ID(required) is a unique variable that is tied to a specific user. For example, this might be a client ID in your database.
VISITOR NAME (optional) is a value that you can pass with your visitor ID, something that would make more sense than seemingly random numbers in graphical reporting.