=SOMMEPROD((N(INDIRECT("'"&nf&"'!"&CAR(65+COLONNE())&LIGNE(4:4)))*N((INDIRECT("'"&nf&"'!"&CAR(64+COLONNE())&LIGNE(4:4)))))/(NBVAL(INDIRECT("'"&nf&"'!"&CAR(64+COLONNE())&LIGNE(4:4)))-SOMMEPROD(NB.VIDE(INDIRECT("'"&nf&"'!"&CAR(64+COLONNE())&LIGNE(4:4))))))