This MB&F Horological Machine 4 Thunderbolt Titanium & Sapphire is rated 9.6 out of 10. It comes with box and undated paper. The HM4 was designed to look like two engines, mounted on their sides, with a structure design to allow them to sit on a person’s wrist. It is estimated that less than a hundred pieces of HM4 variations were made by Max Busser and his team, this piece is highly collectible and extremely rare. A modern day horological art piece.