Unless otherwise agreed, the company price is invoiced in monthly installments, proportionally to its progress. VAT, other taxes and charges, and their modifications, are always at the expense of the co-contractor. Invoices are payable within 15 days of their dispatch, failing which the amounts due will bear, by right and without formal notice, interest at the rate of 8.5% per year, calculated pro rata to the number of days of payment delay. Similarly, amounts due not paid by the co-contractor at maturity are increased by right and without formal notice by a fixed compensation of 10% of the remaining amount due with a minimum of €125.
						
 3 - Price revision
 
								Even in case of absolute fixed price, any modification of wages, social charges, material prices or their transport, gives rise to a price revision to be operated during the invoicing concerned for work executed according to the following formula: p = P x (0.40 x s/S + 0.40 x i/I + 0.20) "P" is the amount of work performed and "p" this adjusted amount. "S" is the average hourly wage fixed by the joint commission, in force on the 10th day preceding the submission of the offer and increased by the global percentage of social charges and insurance admitted on that date by the SPF Economy; "s" is this hourly wage, recorded before the start of work that is the subject of the partial payment request, increased by the aforementioned percentage admitted during this period. "I" is the monthly index fixed by the Construction Materials Mercurial Commission, in force on the 10th day preceding the submission of the offer; "i" is this same index recorded before the start of work that is the subject of the partial payment request, increased by the aforementioned percentage admitted during this period.