What does federal service from date on the Oregon Worksheet refer to?

[MaryK4]

You may be able to subtract some or all of your pension income, including benefits paid to the retiree or the surviving spouse/registered domestic partner. The subtraction amount is based on the number of months of federal service before and after October 1, 1991.

If your service was before and after October 1, 1991, you can subtract a percentage of your pension income based on the number of months of service before October 1, 1991 divided by the total number of months of service. This percentage does not change from year to year. See the example below to determine the correct percentage.