Is it possible subtotals in this way ?

[forstera]

I need to introduct subtotal in my reports. The problem is that  the subtotals can be anywhere. I explain : I've some order lines. Each line type can be a product, a titel or a subtotal. When the line type is product, there's a price. From the beginning of the report, I need that a variable calculate the sum of every line that is of product type. As soon as it is a subtotal line type, I'd like that the amount is displayed than the value reset to 0.

Is it possible to do that ? If yes, can someone give me some help ? There's about 4 hours I'm trying but withou any success ... :(

Per advance, thanks for your help

Arnaud