NVB Tracker 2x24 Doubler can be used with all models of Tracker series (with the exception of NV Tracker 1x24 Goggles) and increases the magnification of these binoculars from 2x to 3.5x. At the same time the NVB Tracker 2x24 Doubler is included to the NVB Tracker 3.5x40 RX unit.