In this example I try to create a trait with this simulation descriptor (it's just for the show, as the result is absurd) :

<BinarySimulationModifierDescriptor TargetProperty="CityFood" Operation="Addition" BinaryOperation="Multiplication" Left="1" Right="$(Turn)" IsBindOnSource="false" Path="EmpireTypeMajor/ClassCity"/>      

It add to cityfood production a bonus = number of the turn.

If we are turn 32, then bonus is +32.

Unfortunately it don't work, "turn" variable, even used in score victory, here can't be acceded.

I tryed with another variable, as I saw it in ClassEmpire, at least, it should be accessible :

<BinarySimulationModifierDescriptor TargetProperty="CityFood" Operation="Addition" BinaryOperation="Multiplication" Left="1" Right="$Property(ClassEmpire:CurrentTurn)" IsBindOnSource="false" Path="EmpireTypeMajor/ClassCity"/>      

But it don't work too.

Why ?

How to access to Turn number for using it somewhere ?

IsBindOnSource="false" is it correct here ?

Finaly I made it work.

Need CurrentTurn var, and IsBindOnSource = True.

But I still need answers for my others questions !