Time to First Byte
TTFB measures the duration from the user or client making an HTTP request to the first byte of the page being received by the client's browser.
Speed Index
Speed Index is the average time at which visible parts of the page are displayed. It is expressed in milliseconds and dependent on size of the view port.
Measuring Performance
• RUM
– Real User Data
– Measured using browser APIs
• Synthetic
– Simulated User Testing
– Simulated using real devices and browsers