Nice question.
Best way is to create a relational DB at a back end so that the values of one field can be auto updated with the values the user substitutes in the front end via a form or any other means.
Else you are also allowed to use scripting which will handle this on the browser side and then you $_POST array to send it to backend via a PHP inferface accessing RDBMS.
Possibilities are enormous. Depends on how you want to code.
For former user triggers. For latter use anything thats convenient for you.
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You can do it with ultimatewb software. It has a forms builder app.
