According to this method...

According to this method, the period of ghaibat-e-sugra comes to seventy four years.During the period of ghaibat-e-sugra. Imam Mahdi (A.S.) himself appointed his deputies from among the righteous shias. Four of them succeeded each other and continued to fulfill the duty of intermediaries. These four personalities conveyed the questions and problems to Imam (A.S.) and brought back the Imam's (A.S.) answers for the people.The first of these deputies was Janab Abu Amroo Usman Bin Saeed Amri.

Before this he was a representative of Imam Hasan al Askari (A.S.)(Ghaibat-e-Tusi Pg. 353) Shaykh Tusi writes:On the fortieth day the shias were sitting in the company of Imam Hasan al-Askari (A.S.), when Imam Askari (A.S.) wished that they recognise his Hujyat after him.....Suddenly a handsome child was brought before them. He resembled Abu Mohammed (A.S.). Then Imam al-Askari (A.S.) said:"He is your Imam after me. And my successor upon you.

Obey him, and do not go astray after me (after my death), otherwise your religion shall be destroyed and you will be annihilated. Know that, after today you shall not see him, even if you spend your whole life for it. Hence, accept what Usman tells you, obey his commands and listen to what he says. Because he is the representative of your Imam and holds the responsibility. (Ghaibat-e-Tusi Pg.

357)After the death of Usman bin Saeed, his pious son, Muhammad bin Usman succeeded his father upon the post of the deputyship of Imam-e-Zamana (A.S.) (Ghaibat-e-Tusi Pg. 362). Shaikh Tusi has recorded the letters sent by Imam Hasan al Askari (A.S.) and Imam Mahdi (A.S.) to Usman bin Saeed and his son Abu Jafar Mohammed ibne Usman for the shias. These letters consists of commands, prohibitions and replies to the questions of the shias.(Ghaibat-e-Tusi Pg.

356).Mohammed ibne Usman passed away from this world at the end of Jamadi-ul-Awwal in the year 304 or 305 A.H.(Ghaibat-e-Tusi Pg.366)During the time of his illness, as he laid on the sick-bed, the shias and their children came and surrounded him. They asked: "If something happens, whom should we consult instead of you?" He answered, " This Abul Qasim Husayn ibn Ruh ibne Bahr Nawbakhti is successor. And he is the intermediery between you and the Master affair (Imam Mahdi a.s.), and his agent.

He is trustworthy and reliable. Consult him, and in case of important matters, rely upon him. I have been ordered to announce this, and I have announced it" (Ghaibat-e-Tusi Pg.