How do I reference instance variables in fields

How do I reference specific instances of an object in a field.

ie if I want to set a variable to the value of an instance variable for an object without picking that object in the logic.

Basically what I want to do is get the sum of all values for an instance variable of an object at any given point in time. Is there a simple way to do that?

Possibly multiplying the variable by object.count.

So Object.count*(variable) = variable that you want to find.

The problem with that is the variable will have different values depending on the instance

Try this:

[attachment=0:3fhkr9uy][/attachment:3fhkr9uy]

Thanks!