I want to define a field, but I do not know the reference data type?

Hi experts,

I want to define a field similar Opportunities field "Sales Unit" at my Custom Business Object

I use code below:

[Label("Sales Unit")] element ZSalesUnit:OrganisationalCentreID;

But the report show is not presented to me.

My Sales Unit Code: 10 - Sale Department, 20 - Service Departemnt, 30 - Developer Department

What is the correct data type I want to chose?

Thank you.

Best regards,

Daniel