This paper proposes a new ergonomic frame to describe the attitude of an input device used for human-machine interface in tele-echography application. The data acquired from medical experts through polling and recording medical trajectories enabled us to design this new system of angles exhibiting a good decorrelation among its degrees of freedom. A decorrelation improvement of up to 83% can be noticed compare to the standard 3-1-3 Euler angles. This new frame can be exploited for low cost man-machine interface design.