Let me give an example. I being doctor visits 4-5 hospital daily. So I have created a library where I save details of patient with services I offered (i.e. consultation, follow up, plaster application,any OPD based procedure etc). Also I need to keep record of fees I am supposed to get as per services offered. What problem I saw was that I had to manually enter final amount rather than it should have been automatically get calculated depending upon services I have selected. I have seen this function in ' Jotforms' app on Google playstore.