This app is using to converting amounts from Carat to Stone as well as converting amounts from Stone to Carat.

First of all, let us talk about Carat type and Stone type:


Carat (ct):

The carat (ct) is a unit of mass equal to 200 mg (0.2 g; 0.007055 oz) and is used for measuring gemstones and pearls.
The current definition, sometimes known as the metric carat, was adopted in 1907 at the Fourth General Conference on Weights and Measures, and soon afterwards in many countries around the world.[i]
The carat is divisible into one hundred points of two milligrams each.
Other subdivisions, and slightly different mass values, have been used in the past in different locations.
In terms of diamonds, a paragon is a flawless stone of at least 100 carats (20 g).




Stone (st):

The stone is an English and imperial unit of mass now equal to 14 pounds (6.35029318 kg).
England and other Germanic-speaking countries of northern Europe formerly used various standardised "stones" for trade, with their values ranging from about 5 to 40 local pounds (roughly 3 to 15 kg) depending on the location and objects weighed.
The United Kingdom's imperial system adopted the wool stone of 14 pounds in 1835. With the advent of metrication, Europe's various "stones" were superseded by or adapted to the kilogram from the mid-19th century on.
The stone continues in customary use in Britain and Ireland used for measuring body weight, but was prohibited for commercial use in the UK by the Weights and Measures Act of 1985.



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So let's start using that.