This is index is the 12 month average of the monthly average yields of U.S. Treasury securities adjusted to a constant maturity of one year.  In plain English, this index is calculated by averaging the previous 12 rates of the 1 Year CMT.   Because this particular index is an annual average, it is more steady than the 1 Year Treasury Index.  It fluctuates slightly more than the 11th District Cost of Funds, although its movements track each other very closely, as shown on our comparison charts.  The terms 12 MTA (12 month treasury average) and 12 MAT (12 month average treasury) are used interchangeably.