code: func (c *PCPCounterVector) Set(val int64, instance string) error {
  	c.mutex.Lock()
  	defer c.mutex.Unlock()
  
  	v, err := c.valInstance(instance)
  	if err != nil {
  		return err
  	}
  
  	if val < v.(int64) {
  		return errors.Errorf("cannot set instance %s to a lesser value %v", instance, val)
  	}
  
  	return c.setInstance(val, instance)
  }
docs: // Set sets the value of a particular instance of PCPCounterVector.