The subtraction amount is based on the number of months of federal service before and after October 1, 1991.
If you do not have any months of service or points earned prior to October 1, 1991, then you cannot take this subtraction.
Federal pension income is pension provided to the user through the federal government. This could be from services with the Department of Agriculture, Air Force, Department of Defense, etc. This would be income paid to the retiree or the beneficiary.