Emulate Book Field
Use this field on the Book Defaults tab to specify whether you want any of your user books (Internal and user-defined books) to emulate another book's default information and whether you want the ACE book to emulate the AMT book’s default information.
When selecting a book to emulate, you are choosing to copy the defaults applied to the emulated book, which are applied based upon what you entered in the Tax book. You can override the applied data in the destination book if appropriate. Generally, once the defaults are applied, any changes you make to the emulated book are not applied to the destination book.
There is one exception: if the emulated book is the Tax book. If you've emulated the Tax book, you can make changes in the Tax Book, then select the Apply Book Defaults command from the Assets menu.