Add Conditional Rules to Form Fields?

Hi again,

I am not sure if there is a plugin or some sort of way I can create conditional rules for the form (front and backend displays).

Basically I am looking to automatically populate a second field input if a condition is met.

e.g.
If “Stand location” [key=’stand_location’] (select) = “Hall 1” then the input field “Stand#” [key=’stand_hall1′] appears below with a prefix S and space for 4 digits.

If “Stand location” [key=’stand_location’] (select) = Hall 3 then
the input field “Stand#” [key=’stand_hall3′] appears below with a prefix HK and space for 4 digits.

You can see it in action here (on another directory I built but prefer yours) http://www.client-url.com/dev/add-directory-listing/ (login details below). And screenshots below too.

If there is an easy way of doing this then please let me know. If not, any guidance on how to achieve this would be super wonderful. It’s the only thing that’s missing on your plugin, as in every other respect, it’s awesome.