Kan (An Unit of Weight and Currency) (貫)
Kan is a weight unit in the traditional Japanese system of weights and measures, and it was also a Japanese currency unit for the silver coin used as the currency by weight before the Edo period. By weighing fundo (counterweight used in currency exchange), we know that 1 kan in the Edo period was set at 3.746 to 3.747 kilograms.
1 kan was, as a weight unit, equalized with 1000 monme (a traditional Japanese weight unit), and in the Meiji period, 1 kan was set at 3.75 kilograms. 1 kan was, as a currency unit, equalized with 1000 mon, and with 100 hiki (mon and hiki were former Japanese currency units). To make a distinction, kan as a weight unit is sometimes called kanme (an abbreviation for 1 kan 'mekata' [weight]), and kan as a currency unit is sometimes called kanmon.
In China, a copper coin called Kai Yuan Tong Bao was minted for the first time in the age of the Tang dynasty, and from the age of Northern Sung dynasty, the coin's weight began to be used as a weight unit called 'sen' (in piyin, 'qian'). This sen was introduced into Japan, where it began to be called monme (written as 匁, originally 文目 in Chinese characters which was an abbreviation for 目方 [mekata; weight] of 1 文銭 [1 monsen; 1 sen coin]).
When a large number of copper coins were carried, it was common that a set of 1000 coins was bundled up with a string at their center holes for convenience of a carry and count and there existed a simpler version of a set of 960 coins, called tanhaku. And this was the kan as a currency unit, and the weight of the 1000 coins became the kan as a weight unit.
As mentioned above, the weight unit of monme had existed, and kan was devised as its 1000 times weight. After joining the Treaty of the Meter, Japan enacted the Weights and Measures Act in 1891, which set 1 kan at 3.75 kilograms or 15 over 4 of 1 kilogram, defined by the international prototype of the kilogram, and equalized 1 monme with one 1000th kan.
The weight units under the traditional Japanese system of weights and measures are as follows:
1 kan = 100 ryo = 1000 monme = 3.75 kilograms
1 ryo = 10 monme = 37.5 grams
1 monme = 10 fun = 3.75 grams
1 fun = 10 rin = 375 milligrams
1 rin = 10 mo = 37.5 milligrams
1 kin = 16 over 100 kan = 600 grams
1 kanmon = 2 koku (before the introduction of kokudaka system [tax and salary system based on the annual yield of rice by koku], the warload's territory was sometimes rated with kandaka system [a system to measure the amount of rice production based on the land size by sen]).
The weight unit of kan was devised in Japan, so it is not seen in other countries where the traditional East Asian system of weights and measures are used. In China, for example, kin (reads as 'jin' in pinyin) was used as a basic weight unit which was equalized with 160 monme (or 160 'sen' [reads as 'qian,' in pinyin] in China). However, as the weight unit of a pearl, monme, along with kan, is still used as an international weight unit.
Officially, 1 kanmon was equalized with 1000 mon, but commonly, 960 mon was regarded as 1 kanmon in the Edo period, and the latter way was called shohaku method. Kan and monme, which were originally the weight units, also served as the currency units of the silver coin used as the currency by weight, and 1000 monme of silver was equalized with 1 kan of silver.