When I define a reference area can you explain exactly what I am trying to achieve with the shape of the blue line showing the average brightness? In one sequence I am working on the brightness does not or should not change so am I looking to achieve a flat blue line?

Thanks.

Larry

you should set the reference area where ideally only the global lightning changes and no movement disturbs that. This is to distinguish flicker from wanted changes. So set the reference area wher the only short term brightness change would be flicker, if any.
Suitable would be a stone or a road or the cloudless sky.
Not a good choice would be clouds, waves, parts where cars or people pass etc.
This will lead to a blue curve with long term changes and short term flickering.
By using deflicker you will remove the latter.