Differential GPS - NOT
Depends upon a fixed station having a known and precise location, somewhere nearby, and thus able to quantify the magnitude and direction of the "lie" or inaccuracy at any given moment. This parameter is then used by the GPS receiver that does NOT know its precise location, so that it can apply the error measured by the reference station to its own computed location, to provide additional accuracy. Operative word is "nearby", else the unknown GPS could be experiencing a totally different error, to say nothing of getting the differential error reading from the ref. station.