Each region handles the Camino differently. This is an example of the concrete posts that Galicia uses. You see one at any place where there is some question about which way to go and at least every half mile.
The distance is down to a yard. I have no reason to doubt it since civilian GPS has that accuracy but I wonder about the logistics of installing them. You would need to take the reading right by the post and it must go a foot or more down into the soil. The metal plaque is securely installed in the cement. This is necessary because people steal them for souvenirs. We walked the Portuguese Camino in 2017 and all the distance plaques in the last 100 km had been stolen. They were not as securely attached as these are, they must have changed their policy to prevent thefts.
I also wonder about the need for one yard accuracy to a city of 100,000 people that probably covers 3-4 square miles but what the heck, why not?