Variable counter

Hi everyone,

I'm not new to storyline but I think the trigger options have changed since I last used them and when I try to look up how to add a count to a variable all of the posts look like they are old and using options on the trigger that I no longer see available.

I'm looking for a simple way to add 1 to a variable. For example my variable TestX will be set to 0 to start. Every time my user opens a new layer, I want that layer's timeline to trigger a +1 to variable TestX. So the next time a layer is opened TestX would equal 1, then the next time 2 and so forth.

Can someone please point out how to add the +1 to a variable in Storyline 360?

Thank you,

Kristen