OnScreenRuler Turns a Display Into a Measuring Tool

Field notes

The ruler offers four calibration routes: automatic detection, device selection, entered screen diagonal, and a physical bank-card reference. The card method uses the standard 85.6 mm width as its known measurement, while the page says calibration is saved in the browser for later use on the same device. Controls also include fullscreen, rotation, popup, and unit switching, making this more than a static ruler image.