Applies provisions governing the computation of an annuity under the Civil Service Retirement System (CSRS) for a federal employee whose service includes service that was performed on a part-time basis to: (1) service performed before April 7, 1986, with respect to basing average pay on the basic pay for full-time service; and (2) service performed after such date with respect to calculating the benefit by prorating total service to reflect part-time service.