Hi, I 'm trying to create a custom field incremental (sequence) that for each product type the incremental field stockable increase its number by one.

First , I created a custom field called ' x_niu ' (char ) which means " Unique identifier number " to be increased for each type " Stockable " product:

Image #1: http://es.tinypic.com/view.php?pic=6ed98i&s=9#.VsxSLj82xC0

Then I created a sequence for the ' x_niu ' field:

Image #2: http://es.tinypic.com/view.php?pic=2dsomc7&s=9#.VsxR0T82xC0

And I 've finally created a method to generate the sequence from the validation : the type of product must be stockable .

Image #3: http://es.tinypic.com/view.php?pic=1y02a1&s=9#.VsxSXT82xC0

In sale.order.form view , specifically the < notebook > sequence shown by all products not only stockables .In this form the only stockable product is "Acido Fosforico 32 K - SQMC"

Image #4: http://es.tinypic.com/view.php?pic=14dhphi&s=9#.VsxSiD82xC0

This is all. Maybe I've more than one error, but because I am new to Odoo .I'll be waiting ansiosament your advice and input. Thanks.