Set default value based on previous entry

The user is adding new records, all of which will have the same value for the date field. After the user enters each record, I use code found here to automatically take the user the the data entry screen for another new record. I would like to set the default value of the date field to be equal to the value of the date entered on the previously saved record. How can I do that without duplicating the record and wiping out the other fields (the user may have finished entering records so I don't want to add the next record; I just want to set the date's default value based on the last record entered)?