If you see values off by about 4 feet horizontally, it is most likely due to a datum transformation issue. GPS/GNSS is referenced to WGS/IGS/ITRF, and the values you typically want to work in are NAD83 (i.e., the current National Spatial Reference System framework). These are two different ellipsoids, separated by about 2m at the earth's center, which means different global separations. Your field software does a transformation on the fly (i.e., the Molodensky transformation). This issue is usually in your rover settings. C4Gnet.XYZ is constrained to NSRS (currently NAD83- 2011), and in some brands of field software, you have to choose “No transformation,” or you will be double transforming, which is about 4 feet horizontally. For example, in some Topcon field software, you choose “No Transformation,” and in some Trimble software, you choose “NAD83” and not “NAD83-2011”. Consult with your equipment vendor if you need help on how to make these setting changes in your rover. If your orthometric elevation values are off between 60-80 feet, that indicates that a geoid model is not being applied in your field software. Again, consult with your equipment vendor on how to add the current geoid model to your rover. The C4G website also has some GEOID Tools that you might find helpful. 

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