Normal cost, called target normal cost in IRC 430(b), is the present value of the benefits expected to accrue during the plan year, plus any plan expenses expected to be paid from plan assets. In a cash balance plan, that is roughly this year's pay credit, projected to retirement and discounted back at the segment rates.
It is the building block of both ends of the range. The minimum required contribution is normal cost plus any shortfall installment. The maximum deductible contribution is normal cost plus the funding target plus a cushion, less assets.
In a new plan's first year, when nothing has yet accrued, normal cost is most of the story: the funding target is zero, so the minimum and maximum sit close together. After that it usually rises a few percent a year, because each year's accrual is a year closer to being paid. Once your benefit reaches the 415(b) limit, after ten years of participation or sooner if pay binds, further accruals and the normal cost that goes with them stop.