How to create a counter to calculate the progress of the training course ?

Hi team,

I would like to create a kind of counter to calculate the progress of the training course. I have 4 independant chapters, and I would like to display 25% progress when 1 chapter is completed, 50% when 2 chapters are completed, and so on...

How can I build it ? using what kind of variables ?

Thanks a lot for your help.

JP