The fund invests in short-term US Treasury bonds. These securities are investment-grade and have one to five years until maturity. The index is market-value-weighted and is usually rebalanced monthly. The fund aims to hold US Treasurys in the same proportions as they are reflected in the index. The Manager may also opt to use a sampling strategy, which uses quantitative analysis to select bonds that resemble index constituents in terms of key risk factors, performance attributes, industry weightings, market capitalization and other appropriate financial characteristics. Sibling fund ZTL provides the same exposure but with maturities of 20+ years, while ZTM holds shorter term bonds with 5-10 years to maturity.