code: function createMeasureTooltip() {
    if (measureTooltipElement) {
      measureTooltipElement.parentNode.removeChild(measureTooltipElement);
    }
    measureTooltipElement = document.createElement('div');
    measureTooltipElement.className = 'ol-tooltip ol-tooltip-measure';
    measureTooltip = new Overlay({
      element: measureTooltipElement,
      offset: [0, -15],
      positioning: 'bottom-center'
    });
    map.addOverlay(measureTooltip);
  }
docs: Creates a new measure tooltip