Log the state as soon as the article has been read.

This captures people who come to us (views) and read the article in full and who do not create an onwards journey.

As per discussion,

 - Tracking using this technique we'll probably will lose some data from 3g/2g connections.
 - We'll capture data from people who view a single article and read it, but not from people who view an article and don't read it.
 - We'll accidentally capture data from people who read an article, visit another, then click back and visit another. So we are only interested in the first entry per user id + url