Using empty graph axes, the resultant pulse varies between 6 m/s - 12 m/s can be seen in the second image below.
The diagrammatic representation showing the two pulses approaching each other can be seen in the first image.
From the image:
Since they are coming from the opposite side, there is a need to balance the free pulse space in between with a slight increase in time, this demonstration is seen in the second image below.
Learn more about pulse rate here: