code: func (c *PCPCounterVector) Val(instance string) (int64, error) {
  	c.mutex.RLock()
  	defer c.mutex.RUnlock()
  
  	v, err := c.valInstance(instance)
  	if err != nil {
  		return 0, err
  	}
  
  	return v.(int64), nil
  }
docs: // Val returns the value of a particular instance of PCPCounterVector.