A computing device , comprising: a first portion comprising a first three-dimensional orientation sensor system ; a second portion comprising a second three-dimensional orientation sensor system , the second portion being rotatable relative to the first portion ; a logic machine ; and a storage machine holding instructions executable by the logic machine to receive data from the first three-dimensional orientation sensor system indicating a three-dimensional orientation of the first portion , and data from the second three-dimensional orientation sensor system indicating a three-dimensional orientation of the second portion ; determine a relative orientation between the first portion and the second portion based on the three-dimensional orientation of the first portion and the three-dimensional orientation of the second portion ; and adjust a function of the computing device based on the relative orientation, characterized by a sensor configured to output an indication that the first portion and the second portion are in a predetermined relative orientation; wherein the instructions are further executable to, responsive to receiving the indication from the sensor , determine an offset between the data from the first three-dimensional orientation sensor system and the data from the second three-dimensional orientation sensor system , wherein the relative orientation is determined based further on the offset. a first portion comprising a first three-dimensional orientation sensor system ; a second portion comprising a second three-dimensional orientation sensor system , the second portion being rotatable relative to the first portion ; a logic machine ; and a storage machine holding instructions executable by the logic machine to receive data from the first three-dimensional orientation sensor system indicating a three-dimensional orientation of the first portion , and data from the second three-dimensional orientation sensor system indicating a three-dimensional orientation of the second portion ; determine a relative orientation between the first portion and the second portion based on the three-dimensional orientation of the first portion and the three-dimensional orientation of the second portion ; and adjust a function of the computing device based on the relative orientation, receive data from the first three-dimensional orientation sensor system indicating a three-dimensional orientation of the first portion , and data from the second three-dimensional orientation sensor system indicating a three-dimensional orientation of the second portion ; determine a relative orientation between the first portion and the second portion based on the three-dimensional orientation of the first portion and the three-dimensional orientation of the second portion ; and adjust a function of the computing device based on the relative orientation, characterized by a sensor configured to output an indication that the first portion and the second portion are in a predetermined relative orientation; wherein the instructions are further executable to, responsive to receiving the indication from the sensor , determine an offset between the data from the first three-dimensional orientation sensor system and the data from the second three-dimensional orientation sensor system , wherein the relative orientation is determined based further on the offset. <EOS>