Help with Straddle Strategy

Hi Guys,

I’m trying to follow your straddle strategy here.

Only problem I’m having working out the ‘range’. I notice that the diagram shows a 15 minute chart on the USDJPY pair.I can see that the range has somehow been identified. The guidance I see is that you need to look at the range 20 minutes before the news time. However, over what period do you look over to determine the ‘range’? the previous 4hrs, 10 candles? 1 day? Please could you help me with how to determine the range correctly, as this looks like a super strategy that I would like to use. Many thanks, N