Hello there. Here is an example i put together to show how it works.
lets say i have 2 flows
Test_Parent_1 ( has a variable, startdate)
Test_Subflow1 (has a parameter,EffectiveStartDate & a variable EndDate)
In Test_Parent_1 flow, startdate is set to : @addranddays(~SDATE~,5,10)@
and the subflow parameter EffectiveStartDate is set to variable startdate.
In my subflow i now use the parameter (EffectiveStartDate) to calculate an end date for the subflow
@addranddays(^EffectiveStartDate^,3650,6000)@ < 21 years
or
@addranddays(^EffectiveStartDate^,7400,9000)@ > 21 years
I have attached a simple example. I hope i havent confused you even more.
regards