WM calculated the fix using data from either Thomson Reuters or EBS (depending on the currency pair). It took snapshots of trade and order rates at one second intervals and calculated the (unweighted) median rate over the minute window. That is, the fix is calculated based on executed prices, in contrast to LIBOR which was a submission-based process.
The slide shows a range of estimates of the natural rate for the euro area. Slide 3. Estimates of the natural rate of interest in the euro area However, the estimates of the natural rate of interest are subject to a lot of uncertainty.