Takes a continuous control signal, and every time that trigger changes, it adds an 'interruption' to the signal whenever an edge detection, positive or negative, occurs.
When you would use this: When a greater than 0 node can't distinguish between +1 or +2, when it changes from 1 to 2 or 2 to 1, it will subtract 1 from whatever value is currently being input. This only works on boolean values.