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readings different from what you expect, you can use tools such as N2KAanalyzer
®
to locate all
sources of the 127258 Magnetic Variation PGN.
4.3 Variation Input via Manual Entry
If no other source of variation is available (i.e., from either the NMEA 0183 or NMEA 2000
®
interface), the SSC300 can be programmed with a fixed variation value for a given location (this
value can be found on most navigational charts). If variation is manually entered into the
SSC300, then it will do the following:
1. Transmit the Heading, Deviation & Variation (HDG) sentence including the variation field
as manually entered over the NMEA 0183 interface if HDG is enabled (see Appendix A
for enabling or disabling NMEA 0183 sentences).
2. Transmit the Heading True (HDT) sentence using variation data as manually entered over
the NMEA 0183 interface if HDT is enabled (see Appendix A for enabling or disabling
NMEA 0183 sentences).
3. Transmit over the NMEA 2000
®
interface the Magnetic Variation PGN (127258) with the
Variation Source field value corresponding to the manually entered variation. The PGN’s
Variation Source field will be transmitted with the lowest possible quality indicator, which
is “Manual Entry”.
WARNING: Magnetic variation changes as your position on the earth changes; therefore,
the variation should be adjusted with changes in position. The SSC300 will not
automatically adjust variation with changes in position; it is the responsibility of the user
to adjust variation with changes in position.
4.4 Variation Source Selection
As shipped from the factory, the SSC300 automatically looks for variation from both the NMEA
0183 and NMEA 2000
®
interfaces. If there is only a single source of variation available (either
from the NMEA 0183 or the NMEA 2000
®
interface), then there is no need to manually select a
variation source. However, if there are multiple variation sources (i.e., variation available from
both the NMEA 0183 and NMEA 2000
®
interfaces) or there is no source for variation (i.e.,
variation is not available from either the NMEA 0183 or the NMEA 2000
®
interfaces), then it is
necessary to select a particular variation source. The SSC300 can be programmed to specifically
use one of three possible variation sources:
1. Variation from Only NMEA 0183 Interface
2. Variation from Only NMEA 2000
®
Interface
3. Variation from Only Manual Entry
The SSC300 can be programmed to accept a specific source for the variation data using one of
two possible procedures.
1. Using a Maretron Display (Section 4.4.1)
2. Through the NMEA 0183 Interface (Section 4.4.2)