First round is getting to know about your past work. Interviewer probes at different points about the work and one should be able to explain the intricacies and other problems in the project/work. One should ideally recall and explain every nit-bit that they have worked on earlier projects; as the interviewer makes up his/her mind based on some small points that you might have said. It is a very adhoc in nature and lucky hit/miss that the company is ok to live with. The decision is made up using this question alone without really validating so many other engineering aspects is far from ideal.