I can't tell you what entity to use but you need some entity that will use dynamic memory allocation (i.e. meaning that it will get it's values during runtime instead of when you compile the map).

The math_counter description is " Holds a numeric value and performs arithmetic operations upon it. If either the minimum or maximum legal value is nonzero, OutValue will be clamped to the legal range, and the OnHitMin/OnHitMax outputs will be fired at the appropriate times. If both min and max are set to zero, no clamping is performed and only the OutValue output will be fired. "

I would try to tie the output of the math_counter to the input of the logic_relay "A message forwarder. Fires an OnTrigger output when triggered, and can be disabled to prevent forwarding outputs. Useful as an intermediary between one entity and another for turning on or off an I/O connection, or as a container for holding a set of outputs that can be triggered from multiple places" Then tie the output of the logic_relay to the logic_case entity