Convert from carat [international] to stone

Unit Definition (carat [international])
The carat [international] is a unit of mass used for diamonds and other precious stones. Originally spelled karat, the word comes from the Greek keration, a carob bean; carob beans were used as standards of weight and length in ancient Greece in much the same way barleycorns were used in old England. Traditionally the carat was equal to 4 grains. The definition of the grain differed from one country to another, but typically it was about 50 milligrams and thus the carat was about 200 milligrams.

Unit Definition (stone)
The stone is a traditional British unit of weight, rarely used in the U.S. Originally the stone varied in size, both from place to place and according to the nature of the item being weighed. A stone of sugar was traditionally 8 pounds, while a stone of wool could be as much as 24 pounds. Eventually the stone was standardized at 14 pounds avoirdupois or approximately 6.350 29 kilograms - a convenient size because it makes the stone equal to exactly 1/2 quarter or 1/8 hundredweight. Today the stone is used mostly for stating the weight of persons or animals.