The Argus 5000 and 7000 have Real-Time Clocks. What purposes do they serve?
The clock (which includes calendar functions) serves two purposes. It keeps track of the date so you can be notified when your database expires. It also reports the time of day (either UTC or Local depending upon how you set it). This time information is used to calculate your ETA to the waypoint. Because the Argus 3000 does not have a real-time clock, it instead calculates ETEm as do many long-range navigation systems.