18 Inches we find Geocaches in some pretty thick stuff. The hand held units don't spec the accuracy tolerance. Its pretty exact


The G-1000 in the plane is good to 18 Inches.


The the units the surveyors use is +/- .250

I thought the standard civilian CA code with selective availability was good to (worst case) about 100 meters. Why would you give away this navigation accuracy to all your friends and foes?

If you know where you are you can use ground based differential signals and other tricks to get better accuracy but a stand alone receiver will not provide a first fix accurate to 18 inches.

U.S. Geological Survey - Global Positioning Application and Practice

They are saying a meter differential grade.

The plane system is Differential Grade with WAAS.

I use my handheld for finding property pins on large acreages, it puts me right on them. 18 inches maybe a stretch. +/- 36 inches yes. Many times we need to dig or scrape for them within 3 feet.

The Russians "GPS" system is Glonass.

https://en.wikipedia.org/wiki/GLONASS

The Chinese system is BieDoun

https://en.wikipedia.org/wiki/BeiDou_Navigation_Satellite_System

The EU has Galileo

https://en.wikipedia.org/wiki/Galileo_%28satellite_navigation%29

Japan, India and France are working systems.

The cat is out of the bag and everyone has a system. In the past to get reception from 6 or 8 satellites was great, now we can get double or triple that and accuracy keeps going up.

I read up on WAAS. This accuracy I believe.

If you think about it it sounds crazy. The government pays for ground stations and satellites to calculate how much they degraded the signal and tell you about it.
Depends on what the "MAN" wants you to have.