Different Billing Number Range

Dear All

   My client want different billing number range

   Example for vehicle sales ( sales area 6100,61,60)

                 For spares sales (sales area 6300,61,60)

    For credit memo want different billing number range ,please guide me ,how i can maintain the different billing number range.

   and how should i maintain different accounting number range which is same as the billing number range.

Thanks and Regards

Bhushan