What can be used to measure scroll depth in Google Analytics?

Event tracking is the correct method because Google Analytics doesn't natively track scroll depth as a standard metric. You need to implement custom event tracking, typically using JavaScript, to fire an event when a user scrolls to a certain percentage of a page (e.g., 25%, 50%, 75%, 100%). This allows you to capture data on how far users are engaging with your content. A custom dimension could be used to store additional information about the scroll event (like the specific percentage scrolled), but it's the event itself that records the action. Scroll depth is not a standard Google Analytics metric, and it is indeed possible to track it.