Calculating custom field value based on update

[JohnCPun]

Hello,

In our Mantis instance we have got two custom enum fields: "business value" and "size".
The two enums contain numeric values which are allowed.

We would like to have a third custom field that is calculated from these two values : "business value" / "size".
This will give us a list of issues that are the most optimal to change (requiring the least amount of work and getting the most return).

I have been trying to get this calculation to work in using the custom_enum_override function in custom_functions.
However when I use the get_value for the custom fields the bug_id is null, which makes it impossible to get the value from the custom fields.

Is there any way to retrieve the current bug_id, so I can get the values from the custom fields?
Or is there a better way to do this? As far as I'm concerned automatically updating the calculated custom field on each save is no problem.

Thanks,

John