static pinchScaleRatio_(event, prevEvent) {
    let distance1 = GestureDetector.distance_(prevEvent);
    let distance2 = GestureDetector.distance_(event);
    return distance1 === 0 ? null : distance2 / distance1;
  }
/**
   * Computes the change in scale between this touch event
   * and a previous one.
   *
   * @param {!TouchEvent} event Latest touch event on the element.
   * @param {!TouchEvent} prevEvent A previous touch event on the element.
   * @return {?number} The ratio of the scale of this event and the
   *     scale of the previous one.
   * @private
   */
Computes the change in scale between this touch event
and a previous one.

@param {!TouchEvent} event Latest touch event on the element.
@param {!TouchEvent} prevEvent A previous touch event on the element.
@return {?number} The ratio of the scale of this event and the
scale of the previous one.
@private
Computes the change in scale between this touch event and a previous one . @param { !TouchEvent } event Latest touch event on the element . @param { !TouchEvent } prevEvent A previous touch event on the element . @return { ?number } The ratio of the scale of this event and the scale of the previous one . @private
static pinchScaleRatio_(event, prevEvent) {
    let distance1 = GestureDetector.distance_(prevEvent);
    let distance2 = GestureDetector.distance_(event);
    return distance1 === 0 ? null : distance2 / distance1;
  }
static pinchScaleRatio_ ( event , prevEvent ) { let distance1 = GestureDetector . distance_ ( prevEvent ) ; let distance2 = GestureDetector . distance_ ( event ) ; return distance1 === 0 ? null : distance2 / distance1 ; }
Computes the change in scale between this touch event
 and a previous one.
Computes the change in scale between this touch event and a previous one .