Calculating multiple variables across layers

Hi everyone!

I'm working on a module that includes a video on the base layer and 10 additional layers.  Each layer above the base displays a single question that is part of a 10 question form, with 8 possible check boxes as answers.  I've created 10 numeric variables with a default value of 0, one for each layer/question, and on each layer I have triggers that adjust the value of the variable depending on what check box is selected.  That's working fine and I know how to add the variables if I have students move sequentially through the module.  I don't want to lock the navigation though, as students need to be able to view the video continuously while they work through the questions.  (The video is of a patient interaction, and each question is a checklist of observations.  The combined total of the questions produces a  score that determines what medical intervention is needed .)  So what I'm struggling with is how to create a "total" variable that continually updates by adding and displaying the combined scores from all layers.  Thanks in advance for any tips or suggestions!