The on-the-run Treasury issues are the most recently auctioned issue of a given maturity.These issues include 3-month, 6-month, and 1-year Treasury bills; 2-year, 5-year, and 10-year Treasury notes; and 30-year Treasury bond.Treasury bills are zero-coupon instruments; the notes and the bond are coupon securities.There is an observed yield for each of the on-the-run issues.For the coupon issues, these yields are not the yields used in the analysis when the issue is not trading at par.Instead, for each on-the-run coupon issue, the estimated yield necessary to make the issue trade at par is used.The resulting on-the-run yield curve is called the par coupon curve.