Section 5(7)(a) in The Assam Economic and Statistical Service Rules, 1973
(a)by promotion against 70% of the vacancies from the select list prepared for this purpose from amongst the Sub-Inspector of Statistics belonging to the Assam Economics and Statistical (junior) Service who have rendered service for a continuous period of seven years as Sub-Inspector and have successfully undergone such training and have passed such departmental examination as may be prescribed by the Government for this purpose;