Besançon Observatory in France first awarded its "Tête de Vipère" hallmark to a chronometer in 1897. Withdrawn during the 1970s, the "viper's head" symbol was revived in 2006 as a guarantee of exceptional precision. Since then, only 500 watches have met the requirements of the 16 days of tests on the watch head, in five positions and at three temperatures. TAG Heuer has chosen Tête de Vipère certification for this anniversary edition of The Carrera Chronograph Tourbillon, originally launched three years ago at a remarkably competitive price. The hallmark is stamped on the bridge and is visible through the sapphire crystal of the case back. This blue ceramic model is issued as a limited edition of 155 pieces, in reference to the Carrera's 55th anniversary.