if (this._units === 'units' && !this._label.hasAttribute('title')) {
        this._label.setAttribute('title', 'Calibration is required to display the area in cm²');
        this._label.style.color = this._colors.error;
      } else if (this._units !== 'units' && this._label.hasAttribute('title')) {
        this._label.removeAttribute('title');