The precision of actual GPS chip sets is better than 2.5m CEP(*) or better than 2m using SBAS -
satellite based differential corrections as WAAS in the US or EGNOS in
Europe. SBAS is standard in these chipsets, but has to be enabled by the system integrator.
Data for the u-blox LEA8 or the SIRF Star V 5e families of products.
(*) CEP= 90% of the time in a circle of that diameter.
Boating we have normally near to ideal conditions for GPS
reception - clear sky, little or no obstruction, little multi path
reception. We can take this precisions as valid.
Implies that our measurement expressed with 3 digits of a minute (=1nm or 1852m) should oscillate by 1 at the least significant digit.
Reading
"001E 57.345" the real value will be something in between the range of
.344 and
.346. Or
.343 and
.347 if we want to take precautions.
Not sufficient for automatic
docking (and has the
dock being surveyed correctly?) but pretty good for navigating
Hubert