Field level access by calculation

[Gilbert13]

Hello, I need to be able to prevent edit a field "Email" for users in a privilege "Appusers" if the result of a calculation in a record is true.

Privilege = Appusers

Fields = Applications::Email, Applications::Signature   /   Calculation =  not IsEmpty (Applications::Signature)

I tried to do this in Custom Record Privileges / Field Access / Custom Field Privileges, but there is no way to use a calculation here.  Please help me find how or literature that explains how to accomplish this.

Thanks

Edited June 1, 2020 by Gilbert13

[bcooney]

Define RLA in Edit Limited calc.