I'm wondering what the best way to do this would be?

I have a field that stores the user's city (for instance - Orlando).

When this user changes their city to a new city (for instance - New York), I would like the initial value (Orlando) to be saved in a separate field.

Basically, rather than just "city", we would have "newCity" and "oldCity". Every time the user changes their city, their old city is recorded in the additional field. This way, we would always be able to access the city that the user had lived in prior to the one they live in now.

I've tried some different combinations of auto actions and query fields, and just can't seem to figure out how this could be accomplished.

Any ideas of how I should approach this issue?

Thank you.