How to create a custom field with logic from two existing custom fields

[Tenzing Doleck]

Hi;

I have created two custom fields ; they are user picker( multiple names)

There is third custom field I would like to create which has some logic i.e it outputs the diff between the above two fields. 

Any help on how one can accomplish this?

[Nic Brough -Adaptavist-]

The most obvious way to do it is to create an Automation that triggers when either of your two fields changes, but I'm not 100% sure you can do the calculation needed.

You might need one of the other scripting apps to do this.