The S&P MERVAL Index (MERcado de VALores, lit. 'Stock Market') is the most important index of the Buenos Aires Stock Exchange. It is a price-weighted index, calculated as the market value of a portfolio of stocks selected based on their market share, number of transactions and quotation price. The base of MERVAL is set at 30 June 1986 = 0.01 Argentine pesos. It is part of a joint-venture between S&P Dow Jones Indices and BYMA. The corporations and weighted prices that compose MERVAL are updated every three months, based on their market share during the previous period.