How does the scroll speed test work?
Choose 5 or 10 seconds, put the pointer over the box and spin the mouse wheel as fast as you can, up or down. The box holds the page still while you scroll, and the clock starts with your first turn. Every movement the browser reports is kept with its time, and the result is worked out when the time is up.
On a touchscreen, swipe up and down in the box instead: the page measures how far your finger travels.
How is scroll speed measured?
A browser doesn't report clicks of the wheel; it reports a distance in pixels, and how far one click scrolls depends on your browser and settings. So the test finds your wheel's own step: the distance most of your scroll events moved. If at least 70% of the events moved a whole number of that step, your wheel is notched, one that clicks as it turns, and the result is steps per second. Spin fast and the browser may report two or three steps in one event; those count as two or three.
Touchpads and free-spinning wheels send a stream of small, uneven distances with no step to count. For them, and for swipes, the result is pixels per second instead, and the page says so.
Why does my scroll speed depend on the mouse?
- The notches. A wheel with firm, widely spaced notches takes more effort per step than a light one. Some mice can switch their wheel between notched and free-spinning; a free spin gives distance, not steps.
- Scroll settings. “Lines per notch” in your computer's settings changes how far a step goes, so it changes the distance, but not the number of steps.
- The finger. Flicking the wheel with the fingertip and letting it run is faster than rolling it notch by notch.
Is this a test of my mouse or of me?
Both, and the result can't pull them apart. Steps per second shows how fast the wheel turned; whether that was your finger or a light wheel isn't something a browser can see. Compare results on the same mouse. For other mouse checks, the Double Click Test finds a button that clicks twice, and the CPS Test times the left button.