They are comparing purely inertial navigation (I assume using the advanced nav boreas D90) and inertial nav combined with gravity map matching.

It is more of a demonstration than a comparison. Pure inertial nav has no way to re zero from an external reference so the error only grows.

Both of these systems are worse than any form of sat nav. But both of them keep working if the sat nav is jammed.

https://doi.org/10.48550/arXiv.2608.25563