"Total" numeric field that sums multiple numeric fields from multiple pages

I have a number of numeric fields that I would like to total up. I have created a numeric field that will serve as the total and need a script that will add them up. All the fields that need to be added have the binding name INTVL_n (INTVL_1, INTVL_2, etc.). The fields also reside on multiple pages.

Thanks!