Columbus supports keywords that override observation standard deviations defined in observation 
records. When one of the following keywords is encountered, the standard deviation (or variance 
where applicable) defined in the keyword, will replace the current standard deviation (or variance) 
in the observation.

Example:

! Establish a standard deviation of 10 seconds for all azimuth observations declared after 
! the _G_AZ_SD record.
_G_AZ_SD; 10

! Azimuth observation set with azimuth standard deviation of 0.1 seconds.
_OBS_AZ_SET; AAA; BBB; 120.0000; 0.1; NOOBS; NOOBS; NOOBS; NOOBS; 0.0; 0.0

! When the above azimuth observation is read, the standard deviation applied to it will be 
! 10 seconds (not 0.1 seconds)

! Turn the override off (for all azimuth observations that follow) by setting _G_AZ_SD to zero.
_G_AZ_SD; 0




_G_AZ_SD; 5.0
Azimuth standard deviation override set to 5 seconds.


_G_GEODESIC_AZ_SD; 2.0
Geodesic azimuth standard deviation override set to 2 seconds.


_G_DIR_SD; 5.0
Direction standard deviation override set to 5 seconds.


_G_BEAR_SD; 5.0
Direction standard deviation override set to 5 seconds.


_G_HA_SD; 2.0
Horiz angle standard deviation override set to 2 seconds.


_G_ZEN_SD; 15.0
Zenith angle standard deviation override set to 15 seconds.


_G_CHORD_SD; 0.003
Chord (slope distance) standard deviation override set to 0.003 active linear units. 


_G_HOR_DIST_SD; 0.007
Horiz distance standard deviation override set to 0.007 active linear units. 


_G_HGTDIFF_SD; 0.002
Height difference standard deviation override set to 0.002 active linear units. 


_G_DN_SD; 0.004
Delta north standard deviation override set to 0.004 active linear units. 


_G_DE_SD; 0.004
Delta east standard deviation override set to 0.004 active linear units. 


_G_DUP_SD; 0.004
Delta up standard deviation override set to 0.004 active linear units. 


_G_GEODESIC_SD; 0.0025
Geodesic distance standard deviation override set to 0.0025 linear units.


_G_X_SD; 0.005
GPS delta X standard deviation override set to 0.005 linear units. This
setting will automatically set non-diagonal correlation elements to 0.0.


_G_Y_SD; 0.004
GPS delta Y standard deviation override set to 0.004 linear units. This
setting will automatically set non-diagonal correlation elements to 0.0.


_G_Z_SD; 0.007
GPS delta Z standard deviation override set to 0.007 linear units. This
setting will automatically set non-diagonal correlation elements to 0.0.


_G_X_VAR; 0.00003
GPS delta X variance override set to 0.00003 linear units. This setting 
will automatically set non-diagonal covariance elements to 0.0.


_G_Y_VAR; 0.00003
GPS delta Y variance override set to 0.00003 linear units. This setting 
will automatically set non-diagonal covariance elements to 0.0.


_G_Z_VAR; 0.00006
GPS delta Z variance override set to 0.00006 linear units. This setting 
will automatically set non-diagonal covariance elements to 0.0.


_G_LAT_SD; 0.004
Latitude coordinate observation standard deviation override set to 0.004 
linear units. This setting will automatically set non-diagonal correlation 
elements to 0.0.


_G_LON_SD; 0.005
Longitude coordinate observation standard deviation override set to 0.005 
linear units. This setting will automatically set non-diagonal correlation 
elements to 0.0.


_G_HGT_SD; 0.008
Height coordinate observation standard deviation override set to 0.008 
linear units. This setting will automatically set non-diagonal correlation 
elements to 0.0.


_G_LAT_VAR; 0.00033
Latitude coordinate observation variance override set to 0.00033 linear 
units. This setting will automatically set non-diagonal covariance elements 
to 0.0.


_G_LON_VAR; 0.00035
Longitude coordinate observation variance override set to 0.00035 linear 
units. This setting will automatically set non-diagonal covariance elements 
to 0.0.


_G_HGT_VAR; 0.00044
Height coordinate observation variance override set to 0.00044 linear 
units. This setting will automatically set non-diagonal covariance elements 
to 0.0.


_G_NORTH_SD; 0.004
North coordinate observation standard deviation override set to 0.004 
linear units. This setting will automatically set non-diagonal correlation 
elements to 0.0.


_G_EAST_SD; 0.007
East coordinate observation standard deviation override set to 0.007 
linear units. This setting will automatically set non-diagonal correlation 
elements to 0.0.


_G_NORTH_VAR; 0.00030
North coordinate observation variance override set to 0.00030 linear 
units. This setting will automatically set non-diagonal covariance elements 
to 0.0.


_G_EAST_VAR; 0.00045
East coordinate observation variance override set to 0.00045 linear 
units. This setting will automatically set non-diagonal covariance elements 
to 0.0.