Righello Online, a ruler on your screen

Field notes

The tool combines a movable ruler with a display-calibration workflow. It can work in millimetres, centimetres, or inches, place the measurement panel against four screen edges, and enter fullscreen mode. Its calibration layer compares browser telemetry with a selected hardware profile and accepts a manually supplied screen diagonal when the detected size is wrong. The page labels the resulting hardware values as estimates, making its limitations visible rather than hiding them behind a single precision claim.