Simrad NSS9 Evo3S Operator's Manual page 48

The Great circle route is the shortest path between two points. However, if you are to travel
along such a route, it would be difficult to steer manually as the heading would constantly
be changing (except in the case of due north, south, or along the equator).
Rhumb lines are tracks of constant bearing. It is possible to travel between two locations
using Rhumb line computation, but the distance would usually be greater than if Great circle
is used.
Arrival radius
Sets an invisible circle around the destination waypoint. The vessel is considered arrived at
the waypoint when it is within this radius.
When you are navigating a route, the arrival radius defines the point at which a turn is
initiated.
The arrival circle (1) should be adjusted according to boat speed. The higher the speed, the
wider the circle.
The intention is to make the autopilot start the heading change in due time to make a
smooth turn onto the next leg.
The figure below may be used to select the appropriate waypoint circle when creating the
route.
Ú Note:
The distance between any waypoints in a route must not be smaller than the
radius of the waypoint arrival circle.
XTE limit
Defines how far the vessel can deviate from the selected route. If the vessel goes beyond this
limit, an alarm is activated.
Arrival alarm
When the arrival alarm is enabled, an alarm is activated when the vessel reaches the
waypoint or when it is within the specified arrival radius.
Magnetic variation
Magnetic variation is the difference between true bearings and magnetic bearings, caused
by different locations of the Geographic and the Magnetic north poles. Any local anomalies
such as iron deposits might also affect the magnetic bearings.
When set to Auto, the system automatically converts magnetic north to true north. Select
manual mode if you need to enter your own local magnetic variation.
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Navigating | NSS evo3S Operator Manual