This metric measures the when user perceives that the primary content of the page actually becomes discernible.
FMP is when the biggest above the fold layout change is evident. The lower the score, the faster the user thinks it loaded.
Quickening the paint brush
Google mentions other components to improve page load time here:
- Tracking FMP using hero elements
- Assessing loading performance in real life with navigation and resource timing
- User timing marks and measures
- A layout-based approach