If you’re inclined to sit on the fence these days in the delicate art of anticipating the next phase of the business cycle, you’ll get no argument from the latest update on the Chicago Fed National Activity Index, a monster index of indexes that encompasses 85 measures of U.S. economic activity. This benchmark has weakened this year but it’s still not flashing a formal prediction of economic contraction. But it’s a precarious existence on this side of the line.

The Chicago Fed index’s three-month moving average slipped to –0.28 in August from –0.27 in July, the Chicago Fed reports. No one will confuse that reading with a healthy economy, but it’s not a recession signal either. Technically, we’re in a “below trend” environment. By the rules of this benchmark, the tipping point is when the three-month average falls below -0.70. The latest reading of -0.28 for August is slightly above that level, but the margin of comfort is minimal. It seems that we’re one exogenous shock away from deep trouble.