The Montblanc Grand Tourbillon Heures Mysterieuses was introduced in 2008 in celebration of the 150th anniversary of the Minerva manufacture. It features a case with a distinct bulge at 6:00, making room for the ‘mysterious’ hour and minute hands. The Grand Tourbillon Heures Mysterieuses uses a balance spring with Phillips curve; the Tourbillon Bi-Cylindrique looks similar yet is fitted with double cylindrical springs.
