Speedometer measures web app responsiveness. Roughly, it simulates a series of user operations on web apps built with various frameworks (as well as vanilla JS), and measures the time it takes to complete them and paint the results to the screen.

The score is a rescaled version of inverse time - if it goes up, that implies the browser can handle more user operations per second, or alternately, it takes fewer milliseconds to complete a user operation in a complex web app.