metodo pert

http://www.google.cl/imgres?imgurl=http://www.yolose.es/imagenes/pert_ejemplo2_01_letras.jpg&imgrefurl=http://www.yolose.es/gestion_pert.html&usg=__DBg3PcVvXbnEuQvCBxP8_HUqZNQ=&h=600&w=600&sz=62&hl=es&start=6&itbs=1&tbnid=Ech8ay6u6P6q8M:&tbnh=135&tbnw=135&prev=/images%3Fq%3Dpert%26hl%3Des%26sa%3DG%26gbv%3D2%26tbs%3Disch:1