In res.partner I added a field : pal_b which relate to collotypes pallet_id.col_lenght. 

When i use this field in other model named Calc, i'm getting an error.

Example is:

class Contact(models.Model):
    _inherit = 'res.partner'
    _description = ' Relation restrictions and groups'

    pallet_id = fields.Many2one(comodel_name='collotypes', String='Logistic Unit')
    pal_l = fields.Float(related='pallet_id.col_length', store=True)
    pal_b = fields.Float(related='pallet_id.col_width', store=True)

#------------------------------------------------------------------------------
class Calc(models.Model):
    _name = 'calc'
    _description = 'Module t.b.v. calculation-functions to-do inherit product-templates'

#-----------------------------------------------------------------------------
    customer_id = fields.Many2one(comodel_name='res.partner', String="Customer")
    pallet_l = fields.Float(compute='_get_pal', string='Pallet lengte', store=True)

 # -----------------------------------------------------------------------------
    @api.multi
    @api.depends('customer_id')
    def _get_pal(self):

        for mat in self:
            customer = mat.customer_id
            mat.pallet_l = customer.pal_l

Error is: 

mat.pallet_b = customer.pal_b
AttributeError: 'res.partner' object has no attribute 'pal_b'

What went wrong, can anybody help?