Patent ID: 8489333

Claim:
An apparatus, comprising: a chassis; two non-gyroscopic acceleration sensors attached to the chassis, the acceleration sensors to obtain primary gravitation field data from within a borehole; one of a first memory to store borehole deviation (DEVI) information and borehole magnetic azimuth (HAZI) information, or a third non-gyroscopic acceleration sensor to obtain secondary gravitation field data and a second memory to store the HAZI information, wherein the HAZI information comprises interpolated information and/or survey information over an interval of the borehole where magnetic field data associated with the chassis and the interval is missing or corrupt; and a processor to couple to the first memory or the second memory and to determine a rotational orientation (AZI) of the chassis relative to an Earth System of Coordinates (ESC) based on the primary gravitation data, the DEVI information, and the HAZI information, or the primary and the secondary gravitation field data and the HAZI information.