I feel like I'm missing something very basic.

If this returns the 30 minute rolling Standard Deviation for price: 

self.AddEquity("SPY", Resolution.Minute) self.spy_std_price = self.STD("SPY", 30, Resolution.Minute)

what is the correlating code for volume?

self.spy_std_volume = self.STD("SPY", 30, Resolution.Minute, Field.Volume)

^^Throws an error...

Author