Bitcoin Reference Rate for the CME Methodology

The BRR is calculated based on the Relevant Transactions of all Constituent Exchanges.
Calculation steps for the BRR on any given Calculation Day are as follows:

1. All Relevant Transactions are added to a joint list, recording the trade price and size
   for each transaction.
2. The list is partitioned into 12 equally-sized time intervals of 5 minutes each.
3. For each partition separately, the volume-weighted median trade price is calculated
   from the trade prices and sizes of all Relevant Transactions, i.e. across all Constituent
   Exchanges. A volume-weighted median differs from a standard median in that a
   weighting factor, in this case trade size, is factored into the calculation.
4. The BRR is then given by the equally-weighted average of the volume-weighted
   medians of all partitions.

Be sure to check out the full documentation here at CME's own site