Slides "viewed" only on first visit?
I'm creating a large training module (will be nearly 400 slides when all is said and done). It's fairly simple in its construction: a main menu slide with buttons linking to a number of sub-modules. At the end of a sub-module, the user is routed back to the main menu to make another selection.
I want each sub-module's button on the main menu to change to a "completed" state only after the user has viewed every slide in that particular sub-module. The easiest way to do this seems to be creating a numeric variable for each sub-module that counts up +1 for each slide viewed, and change the state to "completed" when it reaches the correct number. The problem is that, with the sidebar menu available, the user can click around to various slides at will (this is an option the client wants). So if a user clicks into a given slide multiple times, it will count up +1 each time they visit the same slide - meaning, they can technically reach the number of slide views needed to register as "completed," even if they haven't actually completed the entire sub-module.
So, that brings me to my question... short of creating a unique true-false variable for each and every slide (again, we're talking about a large number of slides), is there a way to track when a slide has been viewed for the first time, and not upon re-visiting?