The Nikkei 225, or the Nikkei Stock Average, more commonly called the Nikkei or the Nikkei index, is a stock market index for the Tokyo Stock Exchange. It is a price-weighted index, operating in the Japanese Yen, and its components are reviewed twice a year. The Nikkei 225 measures the performance of 225 highly capitalised and liquid publicly owned companies in Japan from a wide array of industry sectors. Since 2017, the index is calculated every five seconds. It was originally launched by the Tokyo Stock Exchange in 1950, and was taken over by the Nihon Keizai Shimbun newspaper in 1970, when the Tokyo Exchange switched to the Tokyo Stock Price Index, which is weighed by market capitalisation rather than stock prices. Wikipedia