The original indicator was a histogram exhibiting an above/below zero line visual which illustrated which group was driving the market. The amplitude, or size, of the histogram bar showed the strength during that particular time period.
The current version as noted here is a recent adaptation of the indicator, and much easier to read as it clearly defines the signal. The indicator shows as a green and red crossover, using a zero-line level as the long/short signal when the two signal lines cross.