I'm really in stuck with this issue. Here is the scenario. 

App: apparel costing system.

Form 1: Material which have

Fabric {cotton,silk,fleece..etc}

Price {100,200,300,400..etc} **100usd/1kg for example

Form 2: Product Costing which have

Product Name

Norm {0.3,0.4,0.5} **0.3 mean 0.3kg/product

Fabric : lookup from Form1

Price: fetch record from Form1 with criteria form2.fabric == form1.fabric

Fomula: form2.fabric * norm (product price)

Everything quite good when create new product calculation. BUT here

When I update fabric price from form 1, product price (formula) in form 2 does not update (while it base on form 1). Just when I EDIT the form 2 (re-choose all field,then the new price will be calculated)

So my question is how for auto update new price in form 2 when form 1 is entered new data to an existing record..for example form 1 fabric price of cotton 100usd to 130usd...and product price in form 2 will be re-calculated with new fabric price without edit this form 2. Because if i have 1000 record in form 2,i can not edit it manually for updating new price.

Many thanks for your help.