Task: Question Answering
Input (English): Passage: The size of the indemnity had been the hardest factor to accept for the Tibetan negotiators. The Secretary of State for India, St John Brodrick, had in fact expressed the need for it to be "within the power of the Tibetans to pay" and given Younghusband a free hand to be "guided by circumstances in this matter". Younghusband raised the indemnity demanded from 5,900,000 to 7,500,000 rupees, and further demanded the right for a British trade agent, based at Gyantse, to visit Lhasa "for consultations". It seems that he was still following Lord Curzon's geo-political agenda to extend British influence in Tibet by securing the Chumbi Valley for Britain.  Younghusband wanted the payment to be met by yearly instalments; it would have taken about 75 years for the Tibetans to clear their debt, and since British occupation of the Chumbi valley was surety until payment was completed, the valley would remain in British hands. Younghusband wrote to his wife immediately after the signing; "I have got Chumbi for 75 years. I have got Russia out for ever". The regent commented that "When one has known the scorpion  the frog  is divine". The Amban later publicly repudiated the treaty, while Britain announced that it still accepted Chinese claims of authority over Tibet. Acting Viceroy Lord Ampthill reduced the indemnity by two-thirds and considerably eased the terms in other ways. The provisions of this 1904 treaty were revised in the Anglo-Chinese Convention of 1906. The British, for a fee from the Qing court, also agreed "not to annex Tibetan territory or to interfere in the administration of Tibet", while China engaged "not to permit any other foreign state to interfere with the territory or internal administration of Tibet". 
Question: How many years were between the 1904 treaty and its revision? 
Answer type: Number 
Output (English): 2.