The best brains at Cartier have devised clever ways of making the most of the energy available in the ID Two concept watch. Increased efficiency opens the door to greater miniaturisation, more complications, longer power reserve and durability, not to mention improved timekeeping. To start with, the energy is released in series by two stacked double barrels covered with amorphous diamond-like coating (ADLC) for an extremely hard and low-friction surface. Their four mainsprings are made of glass microfibres in epoxy resin with a high coefficient of elasticity. The combination stores 30% more energy than conventional mainspring barrels of the same size. The next innovation is a differential transmission, which delivers the maximum energy to the balance-wheel. Carbon-coated silicon planetary wheels and pinions – 60% more resistant and 70% lighter than ordinary wheels – orbit a central fixed wheel to transmit power to the balance. Tooth profiles have been updated while the pivots have been given a diamond coating, which reduces friction at the jewel bearings and endstones by a quarter, without the need for oil. Finally, to reduce the energy consumed by the balance, Cartier invented the Airfree™ technique, which removes almost all the air in the watchcase. The balance thus oscillates in a near vacuum with no air resistance, cutting its energy use by 37%. It all adds up to a power reserve of 32 hours in a Cartier-sized wristwatch.