Northrop Grumman Sperry Marine VisionMaster FT, User Manual

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System Radar/Chart Radar User Guide
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Inaccurate
There is a possibility that the data is not accurate, based
on some of the information being supplied by the
sensor. For example, if position data is supplied in a
datum other than WGS84, and the sensor does not
supply the offset needed to adjust it to WGS84, the data
will be considered inaccurate. When this applies, the
data is considered usable, but degraded.
Invalid
The sensor providing the data is indicating that the data
is not valid. When this applies, the data is considered
unusable.
Manual
The data was manually entered. When this applies, the
data is considered usable, but degraded.
Nearly Valid
The source of this data is indicating "Invalid" for some of
the samples it is providing. If a higher percentage of
samples are received with the "invalid" indication, then
the data may be indicated as absolutely invalid, in which
case it will be considered unusable. When "Nearly
Invalid", data is considered usable, but degraded.
Nearly Unavailable
The system has received fewer than the expected
number of samples over a recent timespan. If even
fewer samples are received, the data may become
"Unavailable", in which case it will be considered
unusable. When "Nearly Unavailable", data is
considered usable, but degraded.
Over the FOM
Limit
Position sensors can be configured for a maximum
figure of merit. If a position sensor indicates that its
position data has a figure of merit greater than the
configured maximum figure of merit, then the system will
indicate that the data is "over the FOM limit", which
results in the data being considered degraded.
Questionable
There is a possibility that the data is not valid, usually
because no mechanism is being applied to ensure that
the data was not corrupted during transmission. For
example, this may be indicated if the NMEA messages
providing the data have no checksum (if the system is
configured to allow such messages). Questionable data
is considered usable, but degraded.