Carat (mass) Despite its being a non-metric unit, a number of metric countries have used this unit for its limited range of application. The Board of Trade carat was divisible into four "diamond grains", but measurements were typically made in multiples of carat. There were also two varieties of "refiners' carats" once used in the United Kingdom — the pound carat and the ounce carat. The pound troy was divisible into 24 "pound carats" of 240 grains troy each; the pound carat was divisible into four "pound grains" of 60 grains troy each; and the pound grain was divisible into four "pound
AMS-Flight Carat feather the propeller blades. The Carat's propeller is opened by the centrifugal force on the turning blades, working against a folding force provided by a gas damping spring mechanism. This folding mechanism has the advantage of simplicity, but it means that the engine can not be windmill-started if the battery is flat. Because of the forward pointing blades when the engine is off, the Carat cannot be towed aloft like traditional sailplanes. The first flight was made on 16 December 1997 and the first production model displayed at Aero '99 at Friedrichshafen in April 1999 as the Technoflug TFK-2 Carat.