Scroll wheel test
Scroll over the pad. The page records each wheel event's deltaY and delta mode and counts direction reversals, which helps spot a wheel that jumps backwards. It also guesses whether the wheel is notched or smooth, as a rough heuristic.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Move the pointer over the pad and turn the wheel up and down, slowly then fast.
- Check the last delta, delta mode and the reversal count.
- Press Reset to start a new run.
How it works
Each wheel event adds a sample. Reversals count sign changes of deltaY between consecutive non-zero events. The notched or smooth label looks at the last 200 samples.
Worked example
Five notches down, each 100 px, then one up: deltas 100, 100, 100, 100, 100, -100. There is 1 reversal, the total is 400 px, and with only one distinct size of 100 px the label reads notched.
Tips
- Scroll steadily one way for a few seconds: a healthy wheel shows zero reversals.
- A touchpad produces many small deltas and reads as smooth.
Frequently asked questions
What is a direction reversal?
A reversal is a wheel event whose direction is opposite to the previous one, for example a downward event followed by an upward one. While you scroll steadily one way the count should stay at zero. Occasional reversals can point to a worn encoder.
What are delta modes?
The wheel event reports deltaMode 0 for pixels, 1 for lines and 2 for pages. Most browsers on desktop use pixels, and a typical notch is around 100 px or 120 px, depending on the browser and system.
How does it tell notched from smooth?
By a simple rule: a few identical large steps look notched, many different or small steps look smooth. It is a heuristic and can be wrong, for example when the operating system adds smooth scrolling to a notched wheel.
Why does the page scroll when my pointer is outside the pad?
Only the pad captures wheel events. Everywhere else the page scrolls normally.