Increment numeric variable

Despite a number of forum answers, I still can’t figure out how to increment a numeric variable. The following flow works for toggling the Y/No variable, but it keeps changing the count-up variable to null. Can I do this with the built-in cards, or do I need another app? I was also hoping to avoid having to use a Script.

Make sure you select the variable ‘count-up’ in your formula. It now looks plain text

You’re absolutely right !!! Thanks so much.