Static variable in Formula Node

[P@Anand]

Remove the feedback node and use a shift register and pass through a case structure and in a certain case without passing the wire pass an empty element or zero

[Brad]

I would recommend using a Run LabVIEW VI step instead of the Calculator step. This will allow you to do whatever you want with LabVIEW. For what you're trying to do, I would recommend what others have suggested, using an uninitialized shift register to keep the count and you can pass in a flag when you want the count reset.

Hope this helps,

Brad