Save progression + navigation problem

Hello storyline's community !

Here is the problem :

- I have 1 module

- Divided in 7 chapters (scenes)

- In each slide of the module there is a button "go back to the summary".

- The slide "summary" contains 7 buttons to access each of the 7 chapters (see attach file).

The customer want the following navigation :

• If the learner has begun a chapter => then click to "go back to summary" => and then click on a chapter => he must lands where he was.

For example :

• I am on chapter 2, slide 10 => I click on "go back to summary"=> Then i want to return to the chapter 2 => I must land to chapt 2, slide 10.  

The main issue here is that I can't apply a variable based on the "previous" button. Because if for example :

• I am on chapter 2, slide 10 => I click on "go back to summary"=> Then i want to go to chapter 1 => I must land to chapt 1, slide where i was when i quit chapter 1.  The previous button (or variable) will send me to chapter 2, slide 10....

In few words : storyline must "save/remember" each of the slides i have viewed in order to be able to navigate in each chapter and always arrived where i have stopped before.

Any idea  ? :(