A measure of U.S. manufacturing activity surpassed all expectations last month, jumping to its highest level in three and a half years and, economists say, marking a clear sign the overall economy is in recovery mode.

Economists had expected the Institute for Supply Management’s (ISM) manufacturing index to hit 53 in October, from a reading of 52.6 a month earlier, CNNMoney reported. Instead, the purchasing managers’ group said the index topped out at 55.7, the highest reading since April 2006, when it registered 56.

“This is another clear sign the recession is over, and the recovery has begun,” Adam York, an economist at Wells Fargo, told CNN.

The ISM index is a national survey of purchasing managers in the manufacturing field. Index readings above 50 signal growth, while levels below 50 indicate contraction. Readings below 41.2 generally mean the overall economy is in recession. The index has registered growth for three straight months.

The jump in the index was pushed along by growing production and employment, according to Norbert Ore, chair of the ISM’s manufacturing business survey committee.

“Overall, it appears that inventories are balanced and that manufacturing is in a sustainable recovery mode,” Ore said.

The ISM report comes a week after a government survey indicated that the U.S. economy grew 3.5% in the third quarter, after four quarters of decline.