This excerpt taken from the GPS 10-K filed Mar 28, 2006.
10. COMMENCEMENT OF OBLIGATIONS
The obligations set forth herein shall commence on the Initiation Date or as otherwise specified in Exhibit B.1 (Service Level Matrix), referencing Eff+mos (X). The numbers used in Eff+mos (X) are in the format X where X represents the number of months after the Initiation Date when Supplier will be responsible to provide measurement data in support of the Critical Service Level and Supplier will be responsible for Service Level Credits for any failures to attain the Critical Service Level.