Market Ruler HelpOnce per user
From Market Ruler Help
Once per user refers to how actions in ConversionRuler are recorded, and can be useful when wanting to simply tag whether a particular user first performs an action, not the number of times they have performed an action.
For example, if you wish to determine if a user has made their first order from your store, you could create a First Order action, check Once per user in the settings, and place it on your order confirmation page along with an order tracking snippet.
The first time a visitor orders from your store, the "First Order" action will be recorded.
Every subsequent visit, the "First Order" action will be ignored.
When you run your reports, you can see the number of "First Orders" your campaigns generate!