Custom fields needed improvements

Hi @lubos & @Tut
I think that custom fields is liberator feature in Manager wich allow us to customize our Businesses.
But there’s something could add a value to this feature.

  1. A calculation field : to make some needed, personalized and custom calculations between one or more fields in Manager rather the number and dates in custom fields.
  2. The Ability to select any data that already exists in Manager, e.g. fixes assets, employers, owners, customer, suppliers, invoices and any other data from Manager database.
    In this way the customization will fit all the users without changing the purpose and the developer’s vision in this accounting program.