Portable Air/Fuel gauge?

I use this system for my tuning. I use a trailer hitch 4 wire connector to plug it in when I am using it. When the provided sensor is not in, i just plug the hole with an old o2 sensor.

Works great, price is right.

http://www.glowshiftdirect.com/Elite-Series-Wideband-Air-Fuel-Gauge.aspx