Bumping a 10 year old thread here! The reason being I’m revisiting the old project I described in the original post.
But this time I would have to reverse the process ie. I need to SKIP every 3 frames in order to get back to the original. How would I be able to do that?
Here’s a quick illustration of what I’m trying to achieve:

Also, returning to the original expression: what does the “f%4” do exactly?