'invoiced_rate': fields.function(_invoiced_rate, string='Invoiced', type='float'),
'invoice_method': fields.selection([('manual','Based on Purchase Order lines'),('order','Based on generated draft invoice'),('picking','Based on incoming shipments')], 'Invoicing Control', required=True,
readonly=True, states={'draft':[('readonly',False)], 'sent':[('readonly',False)]},
'invoiced_rate': fields.function(_invoiced_rate, string='Invoiced', type='float'),
'invoice_method': fields.selection([('manual','Based on Purchase Order lines'),('order','Based on generated draft invoice'),('picking','Based on incoming shipments')], 'Invoicing Control', required=True,
readonly=True, states={'draft':[('readonly',False)], 'sent':[('readonly',False)]},