The latest Chicago Purchasing Manager's Index, or the Chicago Business Barometer, fell to 56.4 in April from 62.9 in March, which is still in expansion territory. Values above 50.0 indicate expanding manufacturing activity.

Let's take a look at the Chicago PMI since its inception.

Here's a closer look at the indicator since 2000.

Let's compare the Chicago PMI with the more popular national ISM Manufacturing Index. Both indices clearly follow one another, with the ISM falling slightly lower on average. Note the ISM Manufacturing indicator is through the previous month.