Pathfinder marks a contact as interested in a product if they view it multiple times within a certain time period.
To set the thresholds for this rule, go to Contacts - Settings.
Find the fields for product interest:
The default option is 3 views within 5 days. If you change these settings, the system will recalculate for all your contacts.
You can view a contact's interest in their profile page.
Note: Pathfinder re-checks this rule each day and that the number of days is a rolling total. Therefore, if at any point the contact stops meeting the requirements for a particular product, they will no longer be marked as interested in that product.