Bonds are issued in series, meaning they’re offered for sale in smaller batches over time – i.e., not all $619.7 million would be offered in the bond market at once. For example, the 2008 bond was issued in four series: three issues in 2009, and one in 2011. Because the total amount of the bond package is not taken on as debt all at once, the levy rate can vary based on the amount of debt on the books. Laddering bond sales in series helps keep the levy rate as stable as possible by “spreading it out” over time so tax payers don’t pay for the full amount of debt all at once.