a narrow band displays an "estimated" A/F ratio with a light that phases back and forth based on a narrow-band reading through the o2 sensor. A wideband gives you a real time digital readout thats deadly accurate through a wideband o2 sensor.
A narrowband is nothing more than a lightshow..The gauge doesn't really help unless your a/f is WAAAAAAAAAAAY off so in reality its just there. The wideband will let you know even the SLIGHTEST difference in a/f ratio.
Dont mess with narrow-band...waste of money IMO...im sure many will agree.