What does Gamma Notional mean?
Gamma Notional is the sum of call gamma - sum of put gamma
Why does Gamma Notional matter?
This allows you to estimate whether a stock has a larger call gamma position (if figure is positive) or put gamma position (if figure is negative).
How to use Gamma Notional?
A large positive gamma position infers lower volatility in the underlying. A negative gamma position implies higher volatility in the underlying.