Mouse wheel jumping: what to look for

A “jumping” wheel usually means one of three patterns: the page leaps past content, scrolling briefly reverses, or input arrives in bursts with pauses. This page explains how each pattern appears in the scroll test, without claiming any single run proves a hardware fault.

What jumps look like in the event record

Leaps: a few very large deltas among small ones. Check the peaks row on the dashboard and the replay bar heights — one tall tick among short ones matches a leap.
Reversals: ticks outlined in amber with ↑/↓ labels against the requested direction. A rate under a few percent often traces to smoothing or a mid-run correction; a rate that repeats across browsers deserves a second run.
Dropouts: long gaps in the timing profile despite steady hand motion. If the tab hid or focus left the pad, the timer pauses by design — that gap is procedure, not hardware.

How to test jumping fairly

Run the main scroll wheel test downward for 15 seconds with a slow, even turn.
Save it as Run A, change exactly one condition (USB port first), and record Run B identically on the compare page.
Compare opposite-direction counts and unit types side by side. Different setups get a “not directly comparable” warning — heed it.

Safe steps only

Try another port, another browser, extensions off, one OS scroll-setting change, a dry wipe around a powered-off wheel, and another computer — repeating the same test after each single change. Do not open the mouse, use solvents, or reinstall drivers from unofficial sources on this page's advice. Differences describe browser-observed input; they do not prove a repair.