Jon... I think Barometer is a new sensor for Windows Phone. I remember enjoying it on my Nexus 4. There may not be a lot out there for it yet. I don't believe I've seen Barometer listed as a sensor prior to 950/XL.
You'll want an App for that. And then it will help you calibrate and display data.
I would read the reviews. Probably worth paying to get better results in terms of reporting.