Display · browser observations
Monitor motion clarity & ghosting
How clear do moving edges look on your setup? Use an original ruler pattern to compare what you see before and after changing one display setting. This is an observation aid, not a monitor response-time meter or an aim test.
Compare what you see
Three original ruler sleds move at the same declared speed. Follow one with your eyes through the middle of the field, then repeat while looking at the fixed center marks. Stop if uncomfortable. No clicks or score are needed.
No automatic motion, flashing background or sound. Each run is limited to 15 seconds.
Escape stops motion. Fullscreen is optional, never starts motion, and entering or leaving it stops a run.
Ready. The pattern stays still until you press Start.
240 CSS px/s · right · dark background
Browser cadence: Unknown. Too little, coarse, invalid or interrupted callback evidence. Do not infer smooth physical presentation. Inspect frame pacing.
Elapsed: — / 15 s · 0 callbacks · median callback interval: — (not pixel response)
CSS pixels are not panel pixels. Browser zoom, OS scaling, device-pixel ratio and display size change the physical speed. Keep them fixed. This visual comparison produces no GtG, MPRT, input-lag number, monitor grade or ranking. Nothing is saved or uploaded.
Two ways to observe motion
Pursuit observation: gently follow one ruler sled with your eyes as it crosses the middle of the field. Ignore its wrap at the edges. Compare the clarity of its narrow bars and any trailing or bright/dark halos. Eye-tracking accuracy changes the appearance, so repeat rather than treating one glance as a measurement.
Stationary observation: keep your gaze near the fixed center marks instead of following the pattern. The stepping or repeated images you see are a different viewing condition, not a direct reading of pixel response. Do not equate stationary and pursuit appearances. A screenshot freezes one rendered moment and cannot validate either physical motion clarity or panel timing.
Compare one setting at a time
- Use the same display, refresh setting, browser window, viewing distance, room lighting and pattern speed. Keep browser zoom and OS scaling fixed. Start with the default 240 CSS px/s.
- Press Start, observe comfortably, then Stop or Escape. Runs end after 15 seconds. Reduced-motion users get the same deliberate opt-in; nothing moves on page load.
- Change only one monitor setting, such as overdrive, then repeat the same observation. Use the direction and background controls to inspect different transitions, not to produce a score.
Overdrive can reduce some visible trails but can also introduce bright or dark inverse-ghosting halos (overshoot). The most aggressive setting is not automatically best, and behavior may change with refresh rate. This page cannot identify a panel fault, recommend a repair, select a universal setting or rank monitors.
What the declared speed means
Each sled is 80 CSS pixels wide. Its distance is selected CSS pixels per second × elapsed callback time in seconds, wrapping beyond the clipped field edge. All lanes move at the same speed. Positions are updated from callback timestamps, not a fixed distance per frame; callbacks are not guaranteed presented frames.
A CSS pixel is a browser layout unit, not a physical panel pixel or millimeter. Zoom, device-pixel ratio, OS scaling and monitor dimensions change the physical speed and size. Resizing, zoom/scaling changes detected by the browser, hiding the page or leaving it end the run; it never resumes automatically. Undetectable external display changes still require you to Stop and restart.
Cadence and measurement limits
The same animation loop feeds the shared frame-pacing helper. Cadence is unknown until at least 30 positive intervals span one second without invalid, repeated or whole-millisecond-only steps. A regular whole-ms cadence can also trigger this conservative unknown state. A 95th-percentile interval above 1.2× the median, or any interval above 1.75× the median, flags variable pacing. These are disclosed comparison heuristics, not monitor certification thresholds.
A callback or watchdog gap of at least 250 ms stops motion without a catch-up jump. A 12,000-interval cap bounds memory. Stop, Escape, hidden-page, resize and unmount cleanup cancel scheduling and detach run listeners. Optional fullscreen requires its own button; denial leaves the windowed controls available, and entering or leaving fullscreen stops the run.
This browser does not observe light leaving the panel. There is no numerical GtG (gray-to-gray), MPRT (moving-picture response time), photon latency, input lag or physical refresh measurement here. Sample-and-hold behavior, eye movement, pixel transitions, browser scheduling and panel processing can all affect the appearance. Appropriate external optical equipment and a validated protocol are required before making physical response-time claims. No samples, settings or identifiers are persisted, uploaded or submitted to a leaderboard.
Method sources & design
MDN: requestAnimationFrame documents timestamp-based animation and background pausing. CSS Values: reference pixel explains why CSS pixels are not fixed physical pixels. MDN: Fullscreen API describes deliberate entry and browser-controlled exit. The ruler sled geometry is original to this tool, not copied UFO artwork or a standardized optical test target.