code: function scale(x, y, z) {
           y = typeof y !== "undefined" ? y : x;
           z = typeof z !== "undefined" ? z : x;
           return this._set(this._x * x, this._y * y, this._z * z);
         }
docs: Multiply this vector values by the given scalar
  @name scale
  @memberOf me.ObservableVector3d
  @function
  @param {Number} x
  @param {Number} [y=x]
  @param {Number} [z=x]
  @return {me.ObservableVector3d} Reference to this object for method chaining