Unfortunately I didn't get any instructions with the board but tonight, to my embarrassment, i've figured it out.
I hadn't noticed on my new breadboard the power rails had a break in them. I was feeding power at the top of the board and had placed the sensor at the bottom. It never got any power. The 'fixed' values i was getting was actually the Arduino reading ports with an unpowered device connected.
Now it has power it suddenly works!