For most fields on the sign-up form we can make them required (with the exception of drop-down items like customer referrers (How you heard?). Setting any field as required means that zingfit has to pre-fill the field in the database of existing customers that have left that field empty -- so as an example if the birth date field is to be made required, zingfit would have to fill in all blank fields with "01/01/1900".