Raw wheel events are not a diagnosis. This guide walks through what each metric measures, what a healthy value looks like, and what a bad value tells you about your hardware.
What it measures
How many wheel events the browser received during the most recent second. It is not hardware polling rate — it is the density of input your OS actually delivered.
Healthy looks like
Steady values while you scroll at a constant pace. Values that collapse to zero mid-scroll indicate dropped ticks or a stuttering encoder.
Warning sign
Wild swings during a steady hand, or long gaps of 0 events while the wheel is clearly turning.
What it measures
The signed vertical delta of the most recent wheel event. Standard notched wheels usually emit repeated values (often ±100, ±120 or ±1 depending on OS).
Healthy looks like
The sign stays constant for the whole run when you scroll in one direction.
Warning sign
Sign flips appearing while your finger only ever moves one way — a direct sign of reversed ticks.
What it measures
The largest positive and negative vertical deltas captured in the session. Peaks reveal burst behaviour that averages hide.
Healthy looks like
Max and min both reflect your normal notch size. On a one-direction run only one of them should be large.
Warning sign
Repeated deep peaks in the direction you are NOT scrolling — dirty signal bursts from an oxidized contact.
What it measures
How the browser reports deltas: 0 = pixels, 1 = lines, 2 = pages. It is not a quality score, but it changes the scale of every other delta value.
Healthy looks like
Consistent for the entire session, usually 0 (pixels) on desktop browsers.
Warning sign
Changing mid-session — some accessibility or zoom setting is remapping wheel input.
What it measures
Running totals of vertical and horizontal travel. In a vertical-only test Scroll X should stay near zero.
Healthy looks like
Scroll Y grows steadily; Scroll X stays flat.
Warning sign
Scroll X climbing without Shift-scroll means tilt-wheel noise or a touchpad gesture leaking in. Scroll Y stalling means cancellations — forward ticks being cancelled by reverse ticks.
What it measures
Isolated opposite-sign events inside a run of same-sign deltas — a + + − + pattern. It is the basic "reverse gear while driving forward" check.
Healthy looks like
Zero reverse spikes across the whole run.
Warning sign
Any count above zero. The classic cause is dust or oxidation on the mechanical encoder contacts. Contact bounce produces single-tick spikes; a fully failed channel produces many.
What it measures
Each burst of scrolling is treated as one stroke. A healthy stroke ramps smoothly like a mountain peak: slow, fast, slow — all in the same direction.
Healthy looks like
70/100 and above. Stroke magnitudes stay in a tight band and sign churn inside a stroke is rare.
Warning sign
Below 70 means stroke magnitudes jump around or the sign churns mid-stroke — the wheel skips or drags during continuous scrolling.
What it measures
The tool finds the most common |DeltaY| magnitude (the notch) and measures how many events fall within ±20% of it. High coverage means a crisp detented wheel.
Healthy looks like
70%+ coverage → classified as a standard notched encoder. Low coverage with smooth, varied magnitudes → free-spin / infinity wheel (e.g. Logitech MX Superfast).
Warning sign
A notched wheel with erratic magnitudes has a damaged detent spring or a partially blocked sensor.
What it measures
A weighted composite: direction validity 30%, reverse-spike freedom 25%, stroke & notch consistency 25%, anomaly density 10%, sample quality 10%.
Healthy looks like
90+ = A/A+. 80–89 = B. 70–79 = C (clean soon). 60–69 = D (encoder wear). Below 60 = F (likely failing encoder).
Warning sign
A low score driven by sample quality alone just means "test longer". A low score driven by reversals or consistency means hardware trouble.
What it measures
Confidence in the diagnosis: high needs 40+ events over 15s+, medium needs 15+ events over 8s+, low otherwise.
Healthy looks like
High — the verdict, anomaly count and score are all statistically reliable.
Warning sign
Low — treat the report as a quick screen only and run a 30–60s session for a real diagnosis.
Score 90–100
Healthy wheel. No reverse jumps, consistent strokes, clean notch cluster. Keep it.
Score 70–89
Minor noise. Likely dust in the wheel well. A cold-air blowout or isopropyl swab usually restores a clean signal.
Score 60–69
Encoder wear showing. Intermittent reversed ticks under continuous scrolling. Clean the encoder; expect the issue to return as wear progresses.
Score below 60
Failing encoder. Symptoms you will feel: page bouncing on its own, zoom jumping in CAD/video tools, wrong weapon switches in games. Replace the encoder or the mouse.