A process for evaluating motion signals in three-dimensional space is disclosed. The process includes obtaining a first initial measurement value in a first initial direction which is also a first desired direction; obtaining a second initial measurement value in a second initial direction which is different from the first initial direction; calculating a second desired direction and a second determined value from the first and second initial measurement values, the second desired direction being different from the first and second initial directions; calculating a third desired direction and a third determined value from the first initial measurement value and the second determined value, the third desired direction being different from the first and second desired directions; and converting the first initial measurement value, the second and third determined values into respective first, second and third acceleration values. A device for implementing this process is also disclosed.