Circa 1956. Printed 'Refineria de Petroleo "La Isaura" Sociedad Anonima' cover franked with 1954 40c scarlet (SG 865) tied by boxed 'AVISO LLAMADA DIA HORA' cachet with additional boxed 'HORA DE LLAMADA DESTINATARIO' cachet alongside, both markings in bright magenta with times of despatch added in manuscript. Sent from the Refinery in BAHIA BLANCA to the head office in BUENOS AIRES by private express company with a strip of five 'Express' company numbered labels attached to reverse. A rare and unusual item.