Why do you need a variable to jump to a slide? You can use Jump To Slide.
Lilybiri's blog is the best resource on advanced actions and variables. Many talk about it, but nobody has it covered as comprehensively has her. So, here it is.
She has a PDF that lists system variables and its nitty-gritty. Unfortunately for us, it was hosted on Acrobat.com which is phased out now.
Sreekanth