For the most demanding long term accuracy applications, the basic timing source- be it Rubidium, OCXO or TCXO- is disciplined to the GNSS. This accomplished by adding a GNSS receiver to derive a master timing signal. This signal is used to electronically tune the timing source to the GNSS. Accuracies better than E-12 are possible. Novus offers a range of locked reference performance levels for enhanced stability that includes thermal and mechanical isolation. Novus also offers a dual-time base configuration that adds a second GNSS receiver that is used to monitor the primary frequency reference.