F5X compass - calibration off?

Anyone know how the digital compass works on the 5x?
Does it request GPS?

I was in my basement and I was looking at star/constellation images with a son, and we needed to orient north. I know which we is North in my basement, but was going to use the watch to demonstrate a compass. But no matter which way I turned, it seems like East was always the heading. I even went outside for a brief period.

I rarely if even use that digital compass, but last time I did, I thought it was working. Today. It was east even if I faced North or South.

Ideas?