Validating Responses

I am a research assistant learning ODK on the job, so I apologize if my question seems basic! I'm currently working on figuring out how to validate certain responses. I need the survey to calculate the answers for certain questions, and use a validation tag to ensure it's a certain value. In the case of the survey we're developing, I need to be able to reference a previous (preloaded) response and validate that the answer to the question in the new survey adds up. For example, we have questions about the number household members, household members that have left the household, and new household members. How can I make sure that the preloaded response adds/subtracts members and then uses that new number to validate the new answer given by respondents?

There's no such thing as a bad question, so no apologies needed!

In general, you can use calculate to do math and store values.

So in your example, you'd have a calculate question called new_number. Then in the calculation column, you'd have something like ${preloaded_response} + ${added_members} - $substracted_members}.

Start with a very small form that does some calculates, so you get a sense for how it works, then go from there!

Once you have the new_number stored, then you can use that as a constraint or relevance in another question.