I suggest using the register/set/get variable functions instead, because with execute_calculator code you are unnecessarily forcing the sim to send the expression through the XML evaluator every time, which is not needed if you don’t really need an “expression”, the whole point of this would be that external clients in C++/C# would create their own logic, and they surely could do it so much faster and better and with way more complex logic that the XML expression evaluator could possibly do.