Propane Gauge and regulator question

[niceguyjps131]

I just purchased a craftsman 3/8 regulator with gauge. http://www.sears.com/sr/javasr/product. ... Cookie=Yes
I just wanted to know if you think it would work. The only thing I dont know is that there are 4 ports. I can understand 3 but 4 im not sure. Theres 2 big 3/8 ones on each side but where the gauge goes on top there is one directly underneath it, like for another gauge or something. Is it still useable.

[spudshot]

it should be useable, the 4th port is for another gauge probably, one showing tank pressure, the other one would show the regulated pressure