Still more "more than I expected"

I'm referring to the accuracy of GPS, about which I will never stop feeling awe as a technological and scientific marvel.   I didn't realise, until watching a youtube about its monitoring applications, that high end, scientific research versions of GPS receivers can be this accurate:

High-end users boost GPS accuracy with dual-frequency receivers and/or augmentation systems. These can enable real-time positioning within a few centimeters, and long-term measurements at the millimeter level.  

I have the feeling I knew this before, but had forgotten.    

Here's the video, by the way:

Someone in comments to the video notes this: 

I frequently vacation in coastal Oregon, where earth movement is a big concern. GPS stations (the most accurate in the world) measure earth movement as small as one third of a millimetre and they discovered the study area oscillates east and west every two weeks. Japan uses the same accurate GPS equipment, and I believe Oregon got their equipment from Japan (the US military probably has more accurate stuff). Good post! Thanks for sharing it with us.

Other people question the millimetre accuracy, but it seems not out of the question:

I'd assume it's not just GPS. I'm 99% sure GPS does not provide millimetre level resolution. They're probably using a combination of positioning systems.

HotelPapa100

8 days ago

 @Andy Lord  AFAIK the method involves multiple measurements and statistical evaluation. Means can be vastly more precise than individual measurements.

2

ooooneeee

8 days ago

 @Andy Lord  agreed, using GPS and Galileo simultaneously should give them much higher accuracy.