Keyboard Tester / Scroll wheel test
Scroll wheel test
Roll the wheel one way at a steady pace inside the box. Up and down steps are counted separately, and any step that reverses direction within 50 milliseconds of the last one is flagged. A wheel in good shape adds only to one side and shows no flags.
Roll the wheel here
The page will not scroll while the pointer is in this box. Tilt the wheel sideways to test horizontal scrolling.
Steps
- Up events
- 0
- Down events
- 0
- Horizontal events
- 0
- deltaY
- –
- deltaX
- –
- deltaMode
- –
Direction flips
0 flagged
A flip is an up step straight after a down step (or the reverse) within 50 ms. Scroll one way slowly: flips should stay at zero.
Wheel type (a guess)
–
Event log
What to look for
Scroll down ten steps, then up ten. The Down and Up counts should each move by about what you did, and Direction flips should stay at zero. A flip means that between two steps in the same direction the browser saw a step the other way. That is the typical sign of a dirty or worn wheel sensor, and it is the cause of pages that jump back up while you read.
The bar strip under the box shows the last 24 steps: bars rising on one side for down, the other side for up. A wheel with a steady rhythm draws bars of equal height; a clump of short bars means smooth scrolling or a wheel that spun freely.
Notched or smooth
The tester guesses which kind of wheel you have from recent deltaY values. Notched wheels send the same large value per click, often 100 or 120 in pixel mode. Smooth wheels, free-spinning wheels and trackpads send many small, changing values. This is a guess from a handful of events, so scroll a few more steps if it says to.
Horizontal scrolling
If your mouse has a tilt wheel or a thumb wheel, push it sideways. The Horizontal events counter and deltaX should change. On many mice the sideways tilt only works once the vendor software is installed, and some browsers treat Shift plus the wheel as a sideways scroll.
Fixing a wheel that skips
Unplug the mouse and blow compressed air into the wheel slot while turning it. A cotton swab with a little isopropyl alcohol around the wheel often removes grit. If steps still reverse or vanish, the encoder inside is worn. Check the warranty, or compare behaviour on another computer to be sure the cause is not a driver setting such as scroll acceleration.
Questions people ask
Why does my scroll wheel jump up when I scroll down?
Usually the wheel encoder is dirty or worn and reads a backward step between forward ones. Run this test: scroll down slowly and watch Direction flips. If it counts flips, clean around the wheel with compressed air, and replace the mouse if it persists.
How do I test my mouse scroll wheel online?
Move the pointer into the box and scroll up, then down. The page counts each wheel event, shows deltaY, and flags reversals under 50 ms. Compare the counts with what you did.
What is deltaY and deltaMode?
deltaY is how far the wheel scrolled vertically in one event. deltaMode says the unit: 0 is pixels, 1 is lines and 2 is pages. Most browsers use pixels for mouse wheels.
Is my wheel notched or smooth?
Watch the "Wheel type" guess. Fixed values such as 100 or 120 each step mean notched. Many small, varying values mean smooth or free-spinning. It is only a guess based on the last few steps.