Case management allows you to save data from one form and use that data later on in another form. Here's how to set this up:
Say you want to use the answer to "What is your edd?" in Registration later on in your Followup form.
When data get saved to the case as properties, they're always saved as text. If you reference them in a form, even if you set the data type to be "date" or "int" or whatever is appropriate, they're still really strings. If you want to use it in a calculate or a comparison expression, you have to "cast" it to the desired data type. For example, if you reference a property into the hidden value "date_question", you have to reference it as date(#case/date_question). Other available cast operators are int(), boolean(), number() and string().