Hi,

If you want to put new decimal precision for the field of your custom module then you have to do following things.

1) Create new record of decimal precision using xml file as like below.

        <record forcecreate="True" id="decimal_custom_dp1" model="decimal.precision">
            <field name="name">Custom1</field>
            <field name="digits">4</field>
        </record>

2) Then you can use your newly define decimal precision in you custom field as like below.

import openerp.addons.decimal_precision as dp

. . . .

'custom_field1': fields.float(string='Custom Field', digits_compute=dp.get_precision('Custom1') )

Now, you can see the decimal precision of 'custom_field1' according to set new decimal precision 'Custom1'. I hope it is helpful to you.