code: public <T> void link(PushMeasure<T> measure) {
  		if (linkedMeasures.containsKey(measure)) {
  			// already linked
  		} else {
  			MeasureListener<T> listener = new MeasureListener<T>() {
  
  				@Override
  				public void measureGenerated(T value) {
  					increment();
  				}
  			};
  			measure.register(listener);
  			linkedMeasures.put(measure, listener);
  		}
  	}
docs: If this {@link CountingMeasure} is used to count the number of time a
  {@link PushMeasure} notifies its observers, you can use this method to
  link them. The {@link CountingMeasure} will automatically register a
  {@link MeasureListener} on the {@link PushMeasure} such that, every time
  the {@link PushMeasure} send a notification,
  {@link CountingMeasure#increment()} is called. You can link several
  {@link PushMeasure}s at the same time, but each of their notifications
  will increment the counter, leading to summing their notifications. When
  a {@link PushMeasure} should not be considered anymore, use
  {@link #unlink(PushMeasure)} to remove the link.
  
  @param measure
  the {@link PushMeasure} to link