Average Daily Volume
Our default method for calculating average daily volume is to use the mean volume of the most recent 63 business days. If there is no market data, then we may rely on published historical data (we do this for fx forwards), bid-ask spreads (we do this for bonds), or the volume of the underlier (we do this for CFDs).
For options, we always use the volume of the underlier, delta adjusted. This reflects the liquidity that the fund or market maker would face in trying to hedge this exposure.