By default, you will receive the same benefit each month when you retire. You can choose to receive a higher benefit for a period of time. This can be useful if you need more money immediately after you retire than later. For example, if you still have to pay your mortgage. The reverse is also possible: you receive a lower benefit for a while. This can be useful if your partner is still working. The lowest payment must be at least 75% of the highest payment. In principle, you choose for how long you want a higher or lower benefit. 

Note: this is a one-time choice! Once you have chosen this, it cannot be undone.