I told them my experience with mesh decimation. They told me to explain it on the board. The board was perpendicular to the webcam so I do not think the people watching through the webcam could see me. Including the main technical person. Later on they told me I was a strong candidate for front end(they required experience with QT) but my back end part was poor as I couldnt explain my implementation properly. Make sure they understand your implementation correctly. Write every detail on the board. Make sure the other people watching through the cam also understand your implementation in detail.