The Australia 200 (ASX 200) is considered Australia's leading share market index that measures the performance of the top 200 companies. It is listed on the Australian Securities Exchange (ASX) by means of float-weighted market capitalisation. Since April 2000 it has become the principal investment benchmark in Australia. The number of companies, listed in this index, is variable and should not necessarily comprise of exactly 200. Its composition is revised quarterly. The high rate of market representation is responsible for the two major functions of the ASX 200 index: providing a benchmark for the stock market and giving investors a highly liquid and tradable index.