Hi 

i'm new to Zoho but i like it a lot.

i want to build an app that allows me to manage computer repairs

i've managed to build the forms and a few reports but now i want to add parts management

i have a few suppliers, thats easy to put on a form. also the invoices from those suppliers are easy to register

my problem is with different serial numbers 

something like:

-supplier form with name, address and VAT number

-invoice form with a lookup field to the supplier form and also a invoice date field and a invoice number field

--in this invoice form i can add a invoice line subform ( related to another form created before) to enter products details like reference , description and value

---in the invoice line subform i can add a sn subform to enter different sn# for each reference

how do i manage different sn# for the same reference? tried with another subform but i cannot see the sn subform when inside the lines subform in the invoice form

below is a rough drawing of what i need 

do anyone have some pointers that can help me . Thanks