By John S. McClenahen Like the manufacturing sector of the U.S. economy, non-manufacturing activity, while still growing, slowed in September. The Institute for Supply Management (ISM) reported on Oct. 5 that its non-manufacturing business activity index for September was 56.7%, down 1.5 percentage points from 58.2% in August. New orders for the sector slipped a tenth of a percentage point from August, falling to 58.5% from 58.6%. An index reading above 50% indicates that the non-manufacturing sector of the economy generally is expanding; a figure below 50% signals that it is declining. Of the 17 industry groups within non-manufacturing surveyed by Tempe, Ariz.-based ISM, 13 reported growth in September, two reported contraction and two reported business activity unchanged from August.