private void checkUnitCellOffset() {
   if (symmetry == null || fileOffsetFractional == null) return;
   fileOffset.set(fileOffsetFractional);
   if (unitCellOffsetFractional != fileCoordinatesAreFractional) {
     if (unitCellOffsetFractional) symmetry.toCartesian(fileOffset, false);
     else symmetry.toFractional(fileOffset, false);
   }
 }