I would like to add a percentage symbol (%) to a field of type float in measure in a pivot Table Odoo v8

[![enter image description here](https://i.stack.imgur.com/dMPY1.png)](https://i.stack.imgur.com/dMPY1.png)

I want in this measure column to show number as percentage 

**Result that i have in the table : 50.00**
-------------------------------------------

**Result that i want : 50.00%**
-------------------------------

here is my code xml :

```
<record id="view_order_product_graph" model="ir.ui.view">
     <field name="name">forecast_report.graph</field>
     <field name="model">forecast_report</field>
     <field name="arch" type="xml">
         <graph string="Forecasts Analysis" type="pivot">
            <!--  <field name="date" interval="month" type="col"/> -->
             <field name="forecast_quantity" type="measure"/>
             <field name="product_uom_qty" type="measure"/>
             <field name="forecast_subtotal" type="measure"/>
             <field name="price_total" type="measure"/>
             <field name="percentage_forecast"  type="measure"/>
             <field name="product_id" type="row"/>
         </graph>
     </field>
</record>

```

Code python of the forecast\_percentage : 

```
'percentage_forecast': fields.float('% Sales Forecast', readonly=True,  group_operator = 'avg'),

```

Thank you for your help