Print Geometry

Supported nominal paper dimensions are:

Preset	Width × height (mm)
A4	210 × 297
US Letter	215.9 × 279.4
A5	148 × 210
Legal	215.9 × 355.6

Landscape swaps the page width and height. calculate_layout() returns usable grid and cell dimensions after subtracting margins and header regions. Geometry checks report negative or impossible dimensions and grids exceeding declared print bounds. A small-cell finding is advisory. The margins are assumptions supplied by the manifest, not a claim of universal printer-safe margins.