U.S. manufacturers and trade inventories in Sept. this year kept flat from the previous month, after businesses increased their stockpiles for a 20th consecutive month, the Department of Commerce said in a report on Tuesday. The Sept. inventory figure of 1.533 trillion U.S. dollars also represented a 9 percent increase from a year earlier, said the department. The total business inventories-to-sales ratio, a figure measures the time span of the inventories being sold, dropped 0.1 percentage point from Aug. to 1.28 by the end of September, lower than the level of 1.30 one year ago, noted the report. It is normally interpreted as a positive sign of economy when businesses increase their inventories, but some economists held that businesses might slash inventories in the near future if the economic growth pace slows.