Comparing a study to its historical averages?

[Ishaya]

Hello, my name is Ishaya this is my first post. This is a Thinkscript related question.

I am trying to develop a stock scanner to indicate when a stock price close is inside its Bollinger bands
when the Bollinger bandwidth is less than or equal to 1/4 of its 6 month range.

I have been using the condition wizard and think-script editor. How do I make a condition where I can compare current bandwidth to its historical average, specifically less than 1/4 of its 6 month average?

Thank you!