Access specific field name in a custom function

[jim0203]

There's probably a really simple answer to this, but I can't work it out:

In a custom function, how do I set a variable so it is set to the value of a specific field in the current record? The name of the field is "PK".

[comment]

Why would you want to do this? Usually, you define your custom function to handle a variable, and populate the variable only when calling the function.