Mouse Scroll Wheel Test

This mouse scroll wheel test logs every notch you scroll. Roll the wheel slowly inside the box, one notch at a time, then faster. Each notch adds a bar to the track; a coral bar in a run of indigo means the wheel jumped the wrong way.

Scroll test area

Roll the wheel while the cursor is inside

Up 0Down 0Last delta --

Wheel health

Notches in the last second: 0
Direction reversals: 0

A reversal is counted when the direction flips within 120 ms, which a hand cannot do on purpose.

Live mouse

Test the scroll wheel properly

1. Scroll ten notches down, slowly
Count aloud. The down counter should match exactly and the track should be solid coral.
2. Scroll ten notches up
Same check in the other direction. Any indigo bar during a down run is a reversed notch.
3. Spin it fast
Flick the wheel and watch notches per second. Free-spin wheels show high numbers; notched wheels should stay consistent.

Why this scroll checker finds encoder faults

Reversal detection

A flip faster than 120 ms is physically impossible by hand, so it is flagged as an encoder fault.

Notch track

Forty recent notches are drawn as bars so you can see a stray reversed one at a glance.

Delta readout

See the pixel delta per notch. Inconsistent values hint at a dirty or worn encoder.

Speed in notches per second

Compare smooth-scroll and ratchet modes, or check whether a wheel is skipping under speed.

Scroll wheel terms

Encoder: The rotary sensor behind the wheel. Mechanical encoders wear and produce reversed or skipped notches; optical ones last longer.
Notch: One detent click of the wheel. Most mice send one scroll event per notch.
Scroll delta: The amount the browser is told to scroll per event, in pixels. Usually 100 on Windows and 3 lines on macOS.
Free spin: An unlocked wheel mode on some mice that spins freely for fast scrolling, producing many events per second.

Scroll test questions

My wheel scrolls up when I scroll down sometimes. Is it broken?

That is a reversed notch, the classic sign of a worn mechanical encoder. Cleaning helps briefly; replacement is the fix.

Why are some deltas different sizes?

Operating systems and browsers scale deltas, and acceleration can change them with speed. Direction and count matter more.

Does smooth scrolling affect the count?

No. Each wheel event is still counted once; only the pixel delta changes.

Can I test a trackpad?

Two-finger scrolling sends many small events, so counts will be high. The direction and reversal checks still work.

Fix scroll faults

Random reversals

Blow compressed air into the wheel gap and spin it; if reversals continue, the encoder is worn.

Wheel skips notches when fast

Dust under the encoder or a loose wheel shaft. Clean it and check the wheel does not wobble.

Scrolls far too fast

Scroll speed is set high in the OS or the mouse software. Lower lines-per-notch.

Nothing counts

Keep the cursor inside the box; the test only listens to wheel events over the test area.