How is the Pre-Retirement Survivorship Option figured?

When a married, active employee who was eligible to retire dies, the Pre-Retirement Survivorship Option is calculated as if the employee had retired on the first of the month in which the employee died with an "A" 1/2 Survivorship Option. The employee's spouse is then paid 1/2 of what the employee's reduced pension would have been for the remainder of the spouse's life.