SHANGHAI, Aug 26 (Reuters) - The yuan eased against the dollar on Thursday after China"s central bank set a softer-than-expected official midpoint guidance rate, while investors turned their focus to the U.S. Federal Reserve"s Jackson Hole symposium for central bankers. The People"s Bank of China set the midpoint rate at 6.4730 per dollar prior to the market open, barely changed from the previous fix of 6.4728. But several traders and analysts said Thursday"s official guidance rate came in much weaker than the market expected, a sign that the central bank might not want the yuan to gain too quickly. The midpoint was 31 pips weaker than a Reuters estimate of 6.4699. In the spot market, onshore yuan opened at 6.4744 per dollar and was changing hands at 6.4823 at midday, 64 pips weaker than the previous late session close. Investors are closely eyeing the Fed"s Jackson Hole symposium on Friday for clues on the timing of a tapering of monetary stimulus. The global dollar index rose to 92.875 from the previous close of 92.818, hovering near a one-week low versus major peers amid optimism that the Delta coronavirus variant won"t derail a global economic recovery. The offshore yuan was trading at 6.4813 per dollar. The yuan market at 0422 GMT: ONSHORE SPOT: Item Current Previous Change PBOC midpoint 6.473 6.4728 0.00% Spot yuan 6.4823 6.4759 -0.10% Divergence from 0.14% midpoint* Spot change YTD 0.71% Spot change since 2005 27.68% revaluation Key indexes: Item Current Previous Change Thomson 98.71 98.85 -0.1 Reuters/HKEX CNH index Dollar index 92.875 92.818 0.1 *Divergence of the dollar/yuan exchange rate. Negative number indicates that spot yuan is trading stronger than the midpoint. The People"s Bank of China (PBOC) allows the exchange rate to rise or fall 2% from official midpoint rate it sets each morning. OFFSHORE CNH MARKET Instrument Current Difference from onshore Offshore spot yuan 6.4813 0.02% * Offshore 6.6535 -2.71% non-deliverable forwards ** *Premium for offshore spot over onshore **Figure reflects difference from PBOC"s official midpoint, since non-deliverable forwards are settled against the midpoint. . (Reporting by Jason Xue and Andrew Galbraith; Editing by Simon Cameron-Moore) Our Standards: The Thomson Reuters Trust Principles.