TatMapper stores physical values in millimetres and converts display values using exactly:
1 inch = 25.4 millimetres
Artists can choose Automatic, Inches, or Millimetres. Automatic uses the platform locale. Inch displays include a practical fractional-inch value where useful while preserving a precise decimal/millimetre companion value. Changing display units never changes saved geometry, calibration, Print Setup correction, or PDF scale.