Abstract: A measurement and analysis system for characterizing body core motional acceleration and orientation with respect to gravity, and characterizing the motional acceleration and orientation of an ingestible device relative to the body core with associated activity level, and under some conditions, characterizing the motional acceleration of digestive track lumens relative to the body core with associated activity level. The system comprises an in-vivo ingestible sensing device that travels through the digestive track and an external sensing device attached externally to the body core and each device measures orthogonal acceleration vectors data that are transmitted to a computation device that executes algorithms to determine all characterizations. The benefits of the measurement and analysis system are: 1.) increased understanding of digestive track behaviors, 2.) when combined with ingestible diagnostic systems provides increased accuracy through real time environmental knowledge.