Formulas are not supported for HTML Formscentral forms. You can add formulas to the response table but not the actual form. At this point if you really need the form to have formulas your best bet is to edit your PDF form in Acrobat. From there if you want to collect your data in Formscentral you can then import your PDF and collect data there. Your other option is to collect PDF responses via email. Please note that there are some limitation on field types in PDF that are not in HTML forms. As an examply tables are not a supported field type in HTLM forms.
Thanks for our response. I will try to work it out in adobe acrobat pro XI. I have changed the properties of the first fields into time. The last field has a number property. But when I go to the calculation properties, then it isn't possible to make a minus calculation?
Do I have to work with a adjusted script?