How do “tracked topics” work?

How does the software determine whether to register you as ‘tracking’ or ‘normal’ on a post? I see most posts give a count of new messages, but some do not, and can’t see anything systematic that differentiates those that do and don’t.
Thanks!

If you’ve spent four minutes or more reading a topic, the software will set it to “tracking”

Update counts on tracked topics are highlighted in blue to help you find what you’re personally interested in when browsing through the homepage.

thanks - is there a way to make it default to tracking? i find the update counts quite helpful.

I think the best way to do this would be via your user preferences, where you can set topics to be automatically tracked if they belong to a category you’re interested in:

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gotcha thanks