The GNSS menu is shown in Figure: GNSS/GPS Menu. The menu display depends on the options ordered and external reference inputs. The menu below includes Option 3 with Option 56. On-site frequency calibration is accomplished by connecting the Rubidium MG362x1A signal generator's GNSS/GPS receiver to an outdoor antenna and locking to he satellite signal. The GNSS/GPS receiver provides a very stable and accurate 1PPS clock for recalibrating the internal time base.