The four declared categories
Detented mouse
A wheel used in its stepped or ratcheted mode. Browser event count still must not be treated as a physical detent count.
Free-spin mouse
A wheel used in an unlocked or momentum-like mode. One spin can continue producing input without repeated finger actions.
Touchpad
A pad gesture translated into wheel events by the operating system or browser, often with acceleration and momentum.
Unknown
Use when the device or wheel mode cannot be confirmed. Unknown runs remain useful observations but should not anchor device-specific comparisons.
How the event patterns can differ
| Observation | Detented mouse | Free-spin mouse | Touchpad |
|---|---|---|---|
| Physical action | Stepped wheel rotation | Continuous wheel spin | Finger gesture on a surface |
| Momentum | Usually limited by the wheel mechanism | Can continue after release | Often added by the OS |
| Typical trace shape | May look grouped or discrete | May form dense bursts | May be high-resolution and tapered |
| Reliable inference | None of these shapes proves the hardware category | ||
These are possible patterns, not classification rules. Drivers, OS preferences, browsers, applications, and device firmware can make traces overlap.
Event count is not a notch count
A physical detent does not have a required one-to-one mapping to a web WheelEvent. The input stack may split, combine, accelerate, suppress, or schedule information before JavaScript receives it. Counting received events is deterministic for a captured trace, but describing that number as physical notches would be an unsupported conversion.
The challenge therefore reports browser events per second. A free-spin mouse may generate a very different event stream from a detented wheel, and a touchpad has no wheel notches at all. ScrollTest provides no universal quality band or cross-device percentile for those values.
Delta magnitude needs its unit
Each event reports deltaX and deltaY plus a delta mode: pixels, lines, or pages. Pixel deltas are browser/CSS movement units rather than a physical distance. Line and page values depend on settings and document context. A larger value is not automatically faster, better, or more accurate.
ScrollTest keeps unlike modes separate and displays their labels. The full measurement methodology defines the stored fields and comparison scope.
Direction and momentum
ScrollTest classifies a nonzero vertical delta as up or down. When vertical delta is zero, it reports a nonzero horizontal delta as horizontal-only and no movement on either axis as true zero. System direction settings may change how a vertical sign relates to finger motion. Touchpad momentum and a spinning wheel can continue emitting input after release, so changing physical direction before momentum ends may create an opposite-direction observation without a hardware fault.
During the controlled diagnostic, wait for a complete pause between down and up phases. If reversals persist across deliberate repeated runs, follow the reverse-scroll checklist and compare environments one variable at a time.
Rules for useful comparisons
- Compare detented only with detented, free-spin with free-spin, and touchpad with touchpad.
- Keep the device, connection, browser, OS settings, test intent, duration, and metric version fixed.
- Compare pixel totals only with pixel totals, line with line, and page with page.
- Use at least three valid same-scope protocols; exclude visibility-interrupted or materially delayed samples.
- Read event rate and delta movement as separate measurements.
- Treat an unknown-category result as an observation, not a device benchmark.
What a browser test can answer
ScrollTest can show whether the browser received events, which units and directions it reported, how the delivery intervals varied, and whether the same declared setup produced a repeatable trace. It can flag a pattern worth retesting and produce a local report for support.
It cannot prove that every physical action generated an event, diagnose an internal encoder, identify a device model, establish universal accuracy, or make different input categories directly comparable. For environment-specific limits, see browser compatibility.