How do i make a drop down box only allow the item to be entered once

How do i make a drop down box only allow the item to be entered once. For example I have a number of addresses for job sites that only require one visit. once the job is complete and the submission for that address is complete i would like to be able to ensure we don't get multiple entries for the same site/address.

Thanks Dean.

If you would like to limit the amount of times a selection can be made, I would recommend using one of our widgets that allows for limiting quantity.  The gift registry or appointment slots widget would likely suit your needs best since you only need to allow for the selection to be made once:

https://widgets.jotform.com/widget/gift_registry

https://widgets.jotform.com/widget/appointment_slots

Neither is a dropdown but it will allow for what you are looking for.