<td width="72" align="center"><input type="text" name=trat[{num}]" size="6" value="{trat}" onblur="javascript:Calcolo({num})"></td>
<td width="91" align="center"><input type="text" name="chiu[{num}]" size="6" value="{chiu}" onblur="javascript:Calcolo({num})"></td>
<td width="155"><p align="right"><input type="text" name="p_per[{num}]" size="6" value="{p_per}" style="text-align:right; ">%</p></td>

ok per l'id ma ho provato a dare prova e prova2 ma non cambia nulla!