Silver Cross Simplifix ISOFIX Base The Silver Cross Simplifix ISOFIX Base is designed to be used with the Simplicity Plus Infant Carrier. The Simplifix ISOFIX Base is incredibly easy to use. It\'s installed with a simple one-click attachment and has four indicators which show green when the Simplicity or Simplicity Plus Infant Carrier is correctly installed, guaranteeing a safe and secure fit. For additional safety, there\'s an easily-adjusted leg with a green indicator to show contact with the floor. The Simplicity Plus Car Seat (sold sepearately) is suitable from birth through to 13kg and the Base will run perfectly alongside this.