Scroll Test

How to test your scroll wheel

1. Put the pointer inside the box and scroll down slowly, one click at a time, for about ten clicks. Every click should add one to the Down count and show a ▼ chip.
2. Scroll up the same way. Then scroll quickly in each direction for a few seconds.
3. Watch Wrong-way scrolls. A red chip appears when a notch goes against the direction you were scrolling: that is the classic worn-encoder fault that makes pages jump back.
4. Watch Double steps: a notch that moved twice the usual distance, which means the wheel skipped a step.
5. Press Reset after cleaning the wheel or changing a setting, and test again.

What the scroll test shows

• Up and down counts match your clicks: the wheel encoder is healthy.
• Wrong-way scrolls appear while scrolling steadily in one direction: the wheel encoder is worn or dirty. The mouse sends a notch in the opposite direction every few clicks, which you feel as a page that jerks back. This is the most common scroll wheel fault and it gets worse over time.
• Double steps appear: the wheel sometimes jumps two notches at once. Often dust in the encoder; sometimes a game or browser smooth-scroll setting merging two events.
• Nothing counts for some clicks: missed notches. If you scroll ten clicks and the count says seven, the encoder is skipping.
• Last notch (deltaY) is the distance the browser scrolls per click, in pixels for most mice (100 or 120 in Chrome on Windows, 3 lines on some systems). A free-spinning or smooth-scroll wheel sends many small values, which is normal.

Why a mouse wheel scrolls the wrong way

Most scroll wheels use a mechanical rotary encoder: a small drum with metal contacts that opens and closes two switches as it turns. The order in which they switch tells the mouse the direction. When the contacts wear or pick up dust and skin oil, one switch bounces, and the mouse reads a click backwards. The result is a page that jumps up while you scroll down, which is what this scroll test flags as a wrong-way scroll. Optical encoders, used in some newer and more expensive mice, do not have this problem.

If your wheel scrolls in the wrong direction all the time, that is a setting, not a fault: "natural scrolling" on macOS, or the "Scroll direction" option in Windows 11 mouse settings.

Cleaning a scroll wheel

Unplug the mouse or turn it off. Blow compressed air into the gap around the wheel from several angles while spinning the wheel. Then spin it fast in both directions for twenty seconds to scrape the contacts clean. Test again here. If wrong-way scrolls persist, a drop of contact cleaner on the encoder (this needs the mouse opened) often fixes it for months; replacing the encoder is a cheap repair for anyone comfortable with a soldering iron. Check the rest of the mouse with the mouse tester, the double click test and the polling rate test.

Common problems and fixes

The wheel scrolls back on its own

A worn encoder. Clean it with compressed air and spin the wheel hard in both directions. If the test still shows wrong-way scrolls, the encoder needs contact cleaner or replacement.

Scrolling is jerky or skips lines

Check "Double steps" and missed clicks here. If the test counts every notch correctly, the jerkiness comes from software: turn off smooth scrolling in the browser or the mouse software, or lower the lines-per-notch setting in Windows mouse settings.

The wheel scrolls the wrong way everywhere

That is a setting. On macOS, untick "Natural scrolling" under Mouse in System Settings. On Windows 11, change "Scroll direction" in Bluetooth & devices, Mouse. Logitech and Razer software also have a reverse option per mouse.

Nothing happens when I scroll

Make sure the pointer is inside the box. If the wheel works on other pages but not here, a browser extension may be intercepting wheel events; try a private window.