Manually Calibrated Screen Ruler

How to use Manually Calibrated Screen Ruler

Use a known physical length to adjust a local visual ruler. The initial pixel scale is visibly unconfirmed; you must match the reference line and explicitly confirm it. The report keeps CSS geometry and your manual confirmation separate instead of claiming that a screen’s default CSS millimeter is physically exact.

1. Enter a real known reference length and run the unconfirmed ruler.
2. Adjust the line width to match that physical reference and explicitly confirm the match.
3. Read the generated ticks; recalibrate after zoom, resize, orientation or display changes.

Good to know

• Reference 10–300 mm with at most two plain decimal places; slider 50–1,000 integer CSS pixels. Supported ratio is 1–12 CSS pixels/mm, integer ruler length 10–300 mm and at most 1,800 drawn CSS pixels.
• The default is not physical calibration. Accuracy depends on the user’s known object and alignment, viewing conditions, monitor and browser zoom. Numeric/SVG geometry uses ordinary bounded floating-point coordinates, not a certified measurement instrument.
• Resize and observed visual-viewport changes invalidate confirmation. A display move without a browser event cannot always be detected, so manually recalibrate whenever the display/zoom/setup changes. Calibration is not saved automatically.
• No camera, sensor, location, fullscreen or permissions are requested. Scroll inside the bounded ruler surface if it is wider than the panel; no hardware dimensions are inferred from DPR alone.
• Processing is local. Output is limited to 1,000,000 text characters unless a stricter file limit is stated.