Man Mohan was the maid/housekeeper of the college. He used to help people by ironing clothes, delivering food, washing clothes and helping people finish assignments. Farhan told him his room number, it was with him. Sometimes Millimeter makes jokes like what he did to Raju while he was praying. Because of how he helps people that way everyone calls him Millimeter.
At the end of the movie he joins a school in Ladakh and Pia (Directors Daughter) is feeling surprised about how he knows everyone. He said that he was millimeter and now its centimeter until Farhan and Raju said he was kilometer.