Tape-line calibration

Place both rifle-scope ticks on the actual start and end marks of your tape. Drag the photo to pan, use the zoom slider or wheel to zoom, and rotate until the tape follows the slab's length.

Rotate photo { angleDeg = Number(event.currentTarget.value); draw(); }} /> {angleDeg.toFixed(1)}°

Zoom { zoom = Number(event.currentTarget.value); draw(); }} /> {Math.round(zoom * 100)}%

Tick distance in source photo: {tickDistance.toFixed(1)} px