Name : Manoj Kumar Sinha
Date of Birth : 3-10-1950
Time of Birth : 06:45 Hrs(IST)
Place of Birth : Bhagalpur (India)
Query : when i will be appointed principal of the college where i am serving?

Manoj,
According to Vedic Astrology my observations are as follows:
1. Libra Ascendant and Gemini Moon sign.
2. You are passing through Mahadasha of Mercury and Anterdasha of Sun, which will end in April 2013.
3. One opportunity of promotion is still running till February 2013, if you will miss this chance then your Promotion is due after 21-4-2013 to 21-09-2014.
I can not say about Principal (because I have no idea about your current designation), but certainly you have a very good chance of Promotion, as described earlier.