GPGGA format?

At the end of this post is a definition of the NMEA $GPGGA string. My question is : What does emlid put in field 13?

It does not appear to be age of differential. as it has both positive and negative values.

Emlid GGA string .

NMEA GGA definition
1 = UTC of Position
2 = Latitude
3 = N or S
4 = Longitude
5 = E or W
6 = GPS quality indicator (0=invalid; 1=GPS fgeoSepix; 2=Diff. GPS fix)
7 = Number of satellites in use [not those in view]
8 = Horizontal dilution of position
9 = Antenna altitude above/below mean sea level (geoid)
10 = Meters (Antenna height unit)
11 = Geoidal separation (Diff. between WGS-84 earth ellipsoid and
mean sea level. -=geoid is below WGS-84 ellipsoid)
12 = Meters (Units of geoidal separation)
13 = Age in seconds since last update from diff. reference station
14 = Diff. reference station ID#
15 = Checksum.


In certain situations, age of differential can be negative. This may happen in some setups, as the RTCM data is much faster to process than the raw data.

In your example, the age is 0.0. The 14th field is empty and the checksum is following with no comma.

Thanks Egor,
Turns out I was sampling too quickly and was collecting garbage. I have slowed down my collection and your string follows NMEA protocols perfectly.

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