I've got a repeating section, and a calculated value below the repeating section that calculates one of the fields in the repeating section. It works fine, but ONLY if there's more than one entry in the repeating section.
In the screenshots below, the first one shows if I only have one entry. Notice no calculation.
The second one shows if I add a second entry. Now it adds them.
The formula I'm using is "sum(fieldname)". Not much to it.