The 657 is the larger modification of sinns 656 series this is a pilots watch that comes with various useful complications the timepiece makes use of eta 2824 2 automatic calibre it performs 28 800 vibrations per hour and has 25 bearing jewels one unique feature is the extreme protection from magnetic fields the watch is also equipped with captive pilots bezel with minute ratcheting pressure resistance nickel free case back and scratch resistant sapphire crystal glass with anti reflect