How to calculate arithmetic like addition and subtraction in odk build

How to calculate arithmetic like addition and subtraction in odk build.

You may need to use the 'Calculate' option in the 'Advanced' section, and read up on the ODK XForms Functions Spec. Can you provide a more complete example of what you are trying to do? That is, what are the questions you are asking and what is the calculation you want to do?

I prefer to create forums in Excel using XLSForm. The XLSForm form design documentation is a great guide.