Mouse Scroll Wheel Test
Check wheel direction and look for unexpected reverse events. Choose one direction, scroll steadily in the test area and review the events the browser receives.
Choose a test direction
Start one-direction testing, then scroll continuously in that direction inside the area. Opposite events are marked for review.
Scroll test area
Start a down or up test, then scroll in one direction here.
Test stopped. No wheel events observed.
What this means: opposite-direction events during a guided test are worth checking. The browser receives processed wheel or trackpad events and cannot inspect physical encoder detents.
Wheel observations
Recent wheel event history
Scroll direction is more useful than raw delta size
Browsers report wheel deltas in pixels, lines or pages. This test keeps the browser-reported delta and its unit, while using the delta sign to identify direction. Trackpads can produce different event patterns from a stepped mouse wheel.
Do not treat ordinary direction changes as a fault. A possible reversal is counted only during an active guided test in one direction.
Mouse scroll wheel FAQ
Why scroll continuously in one direction?
A one-direction test makes unexpected opposite-direction events easier to notice than unrestricted scrolling. A reversal is still an observation, not a diagnosis.
Why do wheel delta values vary?
Wheel events can report pixels, lines or pages. Browsers, operating systems, settings, wheel resolution and trackpad gestures all affect the values.
Can this inspect a mouse encoder?
No. The browser sees processed events after device, driver and operating system handling. It cannot inspect individual physical encoder detents.