This index is a trailing three month average (to smooth the volatility) of Michigan’s sales tax revenue. Any number above zero means that sales tax revenue is higher that month than the previous year, and any number below zero means that revenue was below the prior year’s. These are year over year, monthly numbers.
Employment in Michigan: The peak of employment in Michigan was in March of 2000, at 4.89 million people employed. Employment as of March 2010 is 4.25 million. (source)
Local housing price indexes from Zillow (note that Zillow confuses the City of Grand Rapids with Grand Rapids Township).