Go to Settings → Bluetooth & devices → Mouse → scroll the slider for "Scroll inactive windows" or open Mouse properties → Wheel tab → "The following number of lines at a time." The default is 3 lines per scroll notch. You can also change it for touchpad in Settings → Bluetooth & devices → Touchpad → Scrolling. Some applications override this setting with their own scroll speed controls. Gaming mice often have dedicated software (e.g., Logitech G Hub, Razer Synapse) that can configure per-profile scroll settings.

Smooth scrolling is a browser or OS feature that animates the scroll motion between positions instead of jumping instantly. Firefox enables it by default; Chrome uses it in some contexts. For this test, smooth scrolling affects the visual appearance of scrolling in the viewport but does NOT affect the raw wheel event data — the deltaY values captured here reflect raw hardware scroll events regardless of visual smoothing. The scroll event fires at the moment the hardware detects the wheel rotation, before any animation is applied.

DeltaY is the scroll amount reported by the browser's WheelEvent. A positive deltaY means scrolling down, negative means scrolling up. The actual unit depends on the deltaMode property: 0 = pixels, 1 = lines, 2 = pages. Most mice report in pixels (deltaMode 0), where typical values are 100–120 px per scroll notch on Windows, and 0.5–3.0 px per touch on macOS trackpads (which have fine-grained momentum scrolling). High-resolution scroll wheels may report much smaller increments, while "hyper-fast" free-spinning wheels like the MX Master can report very large values.

Premium gaming mice differentiate their scroll wheels in several ways: (1) Stepped vs free-spin — many mice offer both a notched (stepped) mode for precise per-item scrolling and a free-spin mode that spins freely for rapid document or web scrolling. (2) Polling rate — higher polling rate mice report scroll events more frequently. (3) Encoder quality — better encoders reduce "skip" and "jump" issues where scrolling past the intended item. (4) Horizontal scroll — some mice support horizontal scroll (tilt-wheel), useful for spreadsheets and code. Gaming mice like the Logitech MX Master 3 are popular even among non-gamers for their premium scroll feel.

Trackpad scrolling (two-finger swipe on macOS or Windows Precision Touchpad) generates continuous fine-grained WheelEvents with small deltaY increments and built-in momentum (on macOS). This results in hundreds of scroll events with small values (0.5–5 px each) instead of the 100–120 px jumps from a mouse wheel. macOS applies its own scroll acceleration curves, making raw deltaY values inconsistent. This test works with both input types but the results will look very different — trackpad shows many small events vs mouse showing fewer large-delta events.

Horizontal scroll (deltaX) is generated by tilt-wheel mice (tilting the scroll wheel sideways), two-finger horizontal swipe on trackpads, or dedicated side scroll buttons on some mice. This tester currently focuses on vertical scroll (deltaY) which is the most common measurement. If your mouse has a tilt-wheel, you will still see events recorded from horizontal scrolling but deltaY may be 0 for those events. Browser devtools (F12 → Console) can log all WheelEvent properties including deltaX and deltaZ if you need full analysis.