I have added the margin and margin percent columns in the treeview of the Quotations and Sales Ordes pages, and I have also added the "sum" attributes to both columns.

<field name="arch" type="xml">
    <xpath expr="//field[@name='partner_id']" position="after">
        <field name="margin_percent" string="Margin Percent (%%)" groups="base.group_user" sum="Average Margins"/>
        <field name="margin" groups="base.group_user" sum="Total Margins"/>
    </xpath>
</field>

I would like to know if there is a way to change the "sum" attribute of the "Margin Percent" field to contain the average of the margin percents?

Any help is appreciated.