Rotate the rectangle until it follows the slab length. The rectangle sets direction only; you enter length L on the next step.
+Drag each tick to where your tape started and ended.
+The black line is fixed: tilting, dragging and zooming the slab never move it. It stays in the middle of the rectangle.
+Tilt the slab
+← → tilt 1° · Shift+← → 0.1° · or drag the ↻ handle
+Zoom the slab
+Crop fill % global setting
++ settings.crop_fill (default 90). At {Math.round(cropFill * 100)}% the overlay ends sit + {(cropMarginFraction(cropFill) * 100).toFixed(1)}% in from top and bottom. + The 3:4 aspect never changes. Stored PNGs are not re-cropped. +
+