Leica MX400 Operating Instructions Manual page 117

Operator's Manual
tracking performance information. The HDOP and VDOP values
indicate the current Horizontal and Vertical Dilution Of Precision.
In simple terms, these are scaled estimates of error in your position,
based on the number of satellites you are tracking and the geometry
of the satellites relative to your position. The lower the value, the
better (more accurate) the position fix. The VDOP value will
always be higher than the HDOP value. When HDOP value exceeds
10.0, the receiver will stop calculating a position fix. If you are
operating in Auto 2D/3D mode (see CFG1 Position), the receiver
will switch to 2D mode when the VDOP value exceeds 5. In a
normal marine environment, the receiver is operated in 2D only
mode when the receiver is in GPS. In this case,
the VDOP value will read 0.0. Good HDOP
values are those less than 4. The user entered
height for 2D mode is one of the major sources
for position error, so the receiver uses the Auto
2D/3D mode as the default when the receiver is
operated in DGPS mode.
The Used Sats value indicates the number of
satellites used in the navigation filter to calculate your position. It is
possible to see 6 sats tracked on the power bar, and 4 or 5 sats
indicated in the Used Sats. This can be due to a number of reasons.
You might have one or two satellites which are marginal in power
(i.e. they are jumping in and out of track). These are typically
satellites which are low on the horizon, or are being shaded or
blocked by superstructure or terrain. If you are operating in DGPS
mode, you may be operating in a fringe or high noise environment.
If this is the case, you may not be getting DGPS corrections for all
of the satellites you are tracking. You can check this by looking in
the DGPS1 screen. The receiver will make every attempt to provide
you with a DGPS solution. If the minimum number of satellite
corrections to operate in DGPS mode are not received, the receiver
will drop into GPS positioning mode (if DGPS Mode is set to ON
in CFG1 DGPS). Otherwise, the receiver will stop providing
position fixes, if DGPS Mode is set to DGPS Only in CFG1 DGPS.
The Visible Sats value indicates the number of satellites reported in
view and available by the GPS system. This information reflects
what is in the Almanac. This information is normally updated once
a day by the satellite system, but can change at any time at the
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GPS
Version 3.3