Scroll Wheel Test — Verify Direction, Speed & Encoder Health
Scroll up or down inside the test area to measure scroll precision, distance, and direction. Detect skipped lines or reverse scrolling caused by a worn encoder.
Scroll inside this area
Roll up or down to measure scroll precision and speed
Last Direction: Idle
Up Distance
0px
Down Distance
0px
Total Events
0
Peak Velocity
--px/ms
Scroll Event Log
Scroll inside the area above to record events
What is a Scroll Wheel Test?
A scroll wheel test measures the events generated by your mouse's scroll wheel as you rotate it. Each detent (the tactile click felt when the wheel rotates) should generate a consistent scroll event with a fixed delta value. Skipped detents, reversed direction events, or inconsistent delta values are signs of a worn or dirty rotary encoder.
Most desktop mice use either an optical encoder (a notched disc interrupting an LED beam) or a mechanical encoder (metal contact strips). Both wear over time, but mechanical encoders are more susceptible to dust, debris, and oxidation that cause the symptoms this test surfaces.
Why Test Your Scroll Wheel?
Scroll wheels are used hundreds of times per day — for browsing documents, code, web pages, and zooming in design or CAD software. A wheel that skips, reverses, or stutters is a constant productivity drag.
In games, the scroll wheel often binds to weapon switching, zoom, or inventory cycling. A misfiring wheel can cost you a fight. This test surfaces issues before they become permanent: a wheel that occasionally reverses direction today will likely reverse far more often after another month of use.
How the Test Works
The test listens to the browser's wheel events, captured with a non-passive event listener so the page itself does not scroll. Each event provides a deltaY value (positive = down, negative = up) and a high-resolution timestamp via performance.now().
From these we compute total up/down distance in pixels, peak velocity (delta per millisecond), and a per-event log. Comparing the up and down distances after deliberate equal-length scrolls reveals whether the encoder is symmetric. Velocity and delta consistency reveal encoder health — a wheel with a worn detent will produce visibly different delta values for what should be identical rotations.
How to Fix Scroll Wheel Problems
Compressed air: Aim a short blast into the gap around the wheel and rotate it while spraying. Dust is the cause of the majority of scroll-skip issues.
Contact cleaner: For mechanical encoders, a few drops of electronics-safe contact cleaner (DeoxIT D5) into the encoder, followed by rotating the wheel for 30 seconds, can restore reliable contact.
Replacement: Encoders are inexpensive (typically $1–3 for an Alps or TTC unit). Replacement requires desoldering the old encoder from the PCB and is feasible for anyone with basic soldering experience. Free-spin and high-resolution scroll wheels (e.g. Logitech MX Master) use proprietary encoders and usually require manufacturer service.
Frequently Asked Questions
Dust or debris inside the rotary encoder is the most common cause. Try blowing compressed air into the wheel slot. If that fails, the encoder contacts may be worn and need cleaning or replacement.
Check the OS scroll-speed setting and whether 'smooth scrolling' is enabled in the browser. Worn encoder contacts can also produce uneven detent detection — even though every notch should produce the same delta.
This tool focuses on vertical scrolling. Horizontal tilt-wheel testing may be added in the future.
It depends on OS and browser. Most desktop browsers report ~100px per notch (or ~3 lines if line-mode is reported). Free-spin scroll wheels and high-resolution wheels (Logitech MX Master, etc.) produce smaller, more frequent deltas.
Brief reversed events can indicate encoder noise — typical of a dirty or aging optical/mechanical encoder. Persistent reversal usually points to firmware or driver settings rather than hardware failure.