old_x             309 core/gps_math.c         double old_x   = rcb->values[rcb->index].x;
old_x             314 core/gps_math.c         rcb->sx         -= old_x;
old_x             316 core/gps_math.c         rcb->sxx        -= old_x*old_x;
old_x             317 core/gps_math.c         rcb->sxy        -= old_x*old_y;