Compare volatility smiles from bid and ask prices for calls and puts with 29 days to expiration . Compare historical volatility for a reach-back period of 29 days (yellow dot).

When an option price is less than the theoretical value would be if the underlying had an expected volatility of 0%, Marlow negative implied volatility preserves comparative information.

Compare term structures of implied volatility from bid prices of call options with different strike prices to term structure of historical volatility (yellow line).