PHP Gform_product_info use mode with paypal

Hi,

I have made a JS hook to let the customer choose beetween full payment or deposit ("acompte") :

function gform_product_total(formId, total){
if(formId == 10){

			if (jQuery('#input_10_71').val() =='acompte|0'){
				total = total *.30;
			}
	}
	return total;

}

The client chooses in a select list (product with 0,00€ price) the mode (full payment or deposit). If he chooses deposit, I calculate 30% of the total amount.

Now, I have to make the php hook to replicate the behaviour before sending to paypal but I do not understand the parameters I have to deal with to make it.

I have read a bunch of doc about it (form entry, gform..., etc.) but it is still a little bit dark.

Can you show me the way ?

Regards,

Frédéric