Dear Fabio,

     In your article "Clinical stabilometry standardization" published in Gait & Posture*, you wrote: "The ‘‘COP Sway Signal’’, consists of the X, Y time plot of the COP during the test." In my opinion, this definition that does not exclude the signals provided by piezoelectric sensors because they actually give a curve of the temporal evolution of the COP positions X and Y, ALTHOUGH these sensors do not pass the DC component, which is very inconvenient in the clinical stabilometry: you can only be sure of the CoP movements, but not of its position. For the moment, I do not see another definition of the signal that allows to exclude these sensors (?). So it would seem necessary to find a solution in order to say that it is impossible for clinicians to make clinical stabilometry with a platform of forces whose sensors are piezoelectric quartz.

      You also wrote: "The origin of the coordinates is placed on the posterior left corner of the platform with reference to the subject’s position during the test." That seems contrary to your first sentence of § 2: "It is strongly felt that there should be an agreement on standard requirements for instrumental measurement performance (Technical Performance) rather than on device design." It seems to me that if you use the left posterior angle of the platform as the origin of the referential frame, then the geometry of the platform should be described and observed.

      Thank you, by the way, for the time you spent on this important issue of the clinical stabilometry standardization and if I would like to discuss what you wrote it is only in order to move more surely toward the solution of this problem.

Nice to hear from you.

Gagey Pierre-Marie

* Scoppa F, et al. Clinical stabilometry standardization. Gait Posture (2012), http://dx.doi.org/10.1016/ j.gaitpost.2012.07.009