On July 31, 2001, the Department of the Treasury began the weekly issuance of 4-week bills. On August 27, 2001, the Treasury stopped reporting secondary market yields for 1-year Treasury bills, the final issuance of which was on February 27, 2001. Effective with the issue of September 4, 2001, the H.15 statistical release reflects these changes by reporting the secondary market rate for 4-week bills and by no longer reporting the secondary market rate for 1-year bills. In addition, the H.15 now reports a 1-month constant maturity rate, which the Treasury began calculating when it introduced the 4-week bill.