Raymarine RC400 Owner's Handbook Manual page 85

Chapter 5: Operation 75
The range scale automatically scales for distance. The ranges shown are
1nm, 4nm, 20nm, 40nm, 100nm, 200nm, 400nm, 1000nm, 2000nm,
4000nm. In each case the range scale has graduations at ¼, ½ and ¾ of the
current scale.
The steering instruction for the BDI display uses the deviation from
vessel bearing to waypoint bearing to instruct you to turn the vessel
towards the target waypoint. This is different from the steering
instructions in all other display modes, which use the XTE to assist you in
steering the vessel back towards the rhumbline between origin and
destination.
The steering instruction is STEER PORT if the waypoint line is 1° or more
to port, STEER STARBOARD if the waypoint line is 1° or more to starboard
or ON COURSE if the waypoint line is dead ahead. If no GoTo or Follow is
in progress, the steering instruction is NOT TRACKING, no steering arrows
are shown, but the rhumb line indicator is shown.
The graphical steering indication will place arrows either side of the
steering instruction and pointing towards it dependent on the difference
between COG and bearing to Waypoint. The first arrow is shown when
the difference reaches 5° and thereafter at 5° intervals.