The Chinese currency renminbi (RMB) or the yuan Monday gained 15 basis points from the previous trading day to hit a new high of 6.4988 per US dollar. The yuan first broke the symbolic 6.50 ratio against the US dollar on April 29 when it was set at 6.4990. The yuan exchange rate has appreciated by almost 1.9% against the dollar since the start of this year. It has also risen by nearly 5% against the greenback since June 19 of last year when the People\'s Bank of China the central bank announced that it would make its exchange rate formation mechanism more flexible. CCB International Research Managing Director Su Guojian said a weak dollar is the main reason the yuan has kept appreciating against the dollar recently. As the third round of the China-US Economic and Strategic Dialogue opens Monday and Tuesday in Washington DC it is expected the renminbi exchange rate will be one of the issues on the agenda China\'\'s news agency (Xinhua) reported. On China\'\'s foreign exchange spot market the yuan can rise or fall 0.5% from the central parity rate each trading day. The central parity rate of the RMB against the US dollar is based on a weighted average of prices before the opening of the market each business day.