That's helpful; so presumably for the same reason that gyrocompasses function (self-aligning vis-a-vis the local gravity vector). A part of me was subconscious

That's helpful; so presumably for the same reason that gyrocompasses function (self-aligning vis-a-vis the local gravity vector). A part of me was subconsciously entertaining that a subsystem of the IMU / INS was actually being used to provide gravimetric navigation (producing a coarse global position update de novo rather than correct for an error-prone open-loop one from an a priori generated gravity map). a la https://ieeexplore.ieee.org/document/9059124 https://ieeexplore.ieee.org/document/9059124 or https://www.researchgate.net/publication/343278497_Analysis_of_structure_and_algorithm_features_of_new_type_strapdown_gravimetric_navigation_system https://www.researchgate.net/publication/343278497_Analysis_...