Just define the band height of the detail band to be half of the height of the page (less any height you have for a page header and/or page footer).
>I have a table which contains records of my students
>Every record is a studend
>I have to print certificates so that it prints two certificates in a A4 page,
>because the certificate is small
>
>So in 10 pages I would have 20 certificates
>
>How can I do ?
>
>Moses