Set digits on float field in xml

I need a set digits on float field in xml. In python we can set digits 开发者_如何学Golike this

'data': fields.float('Data', digits=(16,4))

How to set digits on float field in xml in openerp 6?

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From an OpenERP XML file :

<group colspan="2" col="2" groups="base.group_extended">
                            <separator string="Weights" colspan="2"/>
                            <field digits="(14, 3)" name="volume" attrs="{'readonly':[('type','=','service')]}"/>
                            <field digits="(14, 3)" name="weight" attrs="{'readonly':[('type','=','service')]}"/>
                            <field digits="(14, 3)" name="weight_net" attrs="{'readonly':[('type','=','service')]}"/>
                        </group>

I hope it will help you !