-Double_t AliMUONSurveyUtil::ypCenter(Double_t *x, Double_t *par){
- // par : x1l, y1l, z1l, x2l, y2l, z2, lpsi, tht,
+Double_t AliMUONSurveyUtil::YpCenter(const Double_t *x, const Double_t *par) const{
+ /// Returns center y position using y coord. of 2 button targets. + solution.