How can I control a progress bar on my form from another class I created?

For example, my main form calls a function in another class called SectionLister and in that class I have calls to other functions in another class called SubSectionLister. SectionLister figures out how many subsections it needs to parse using a hashtable with subsection URLs in it, and I want to be able to set the progress bar to the number of entries in the hashtable, then move the bar each time SubsectionLister.List is called with a value from the hashtable.

So I tried to Dim progressbar as formMain.progressBar1 but I can't. What's the right way to do this?