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ScreenRuler

Calibrate once, then measure anything on screen

1 · Calibrate

Put a real bank card flat on the screen and drag the slider until the dashed box exactly covers its long edge.

Card width on screen

Or from a known length: mm between A and B

2 · Measure

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Marker A Marker B

Measurements

Reference sizes

Tap a row to set marker B to that length — handy for a quick sanity check.