> not the stated 1m per 70km travel, surely I don't think that's what they claim. They write "tracking capacity to within a few arc-seconds, equivalent to 1 me

> not the stated 1m per 70km travel, surely I don't think that's what they claim. They write "tracking capacity to within a few arc-seconds, equivalent to 1 meter at a distance of 70 km.", so I interpret that as a way of visualizing how small of an angle a few arc-seconds is. This provides an absolute navigation reference, so a relative error after a certain distance traveled doesn't make sense either. The final navigation system would use inertial navigation combined with this.