Creating counter

[AlexShevyakov]

Hi,

In my app, a user selects a event number and provides description for this event. Event numbers are simple list 1,2,3,4 etc to 30. I made it a dropdown enum field. However, I also need to ensure that the user cannot select the same event number twice AND cannot select a value less than the latest selected event number, i.e. cannot select 2 when the latest was 3 for instance.

Something like VALID IF [THIS VALUE] > MAX Value FROM table_of_values