PURPOSE: A method for realizing an electronic blackboard using an overlay technique is provided to make a teacher give a lecture efficiently by displaying a screen for the teacher to a teacher's monitor and not displaying the screen to the trainee's monitor as using the graphic overlay technique. CONSTITUTION: It is checked that a computer system of the electronic blackboard supports various functions needed for the overlay technique(S110). In case that the computer system supports the functions, a display window such as a toolbar or a sub window shown to only the teacher's screen is made by using a program making tool or a lecture plan making tool of the electronic blackboard(S120). Display window information is stored in an overlay memory space of the computer system(S130). When the display window information is displayed to the monitor, the display window information stored in the overlay memory space is output to the monitor of the lecture and is not output to the monitor of the trainee by turning off the overlay output of a secondary port(S141).
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