Chalk and blackboard presupposes that the students will write down what is written on the blackboard. Overheard projector has two advantages. The first is speed, since the lecturer can present all the information he would fill the blackboard with, on just one transparency.

This technology gives a lecturer much more flexibility. It enables him/her to present the introduction and goals of the lecture quickly and easily, as well as to clearly emphasize the most important parts of the lecture. A lecture can be rich in examples, and experience tells us that the choice of examples for the presentation is often harder than their presentation itself.

Professor's notes i.e. copied transparencies become the authorized version of materials which accompany the text-books. These materials can free students from having to copy from the blackboard and make it easier for them to pay attention to the lecture.