Whiteboard
Whiteboards became commercially available in the early 1960s, but did not become widely used until 30 years later. Early whiteboards needed to be wiped with a damp cloth and markers had a tendency to leave marks behind, even after erasing the board. Dry-erase markers for whiteboards were invented in 1975.
Interactive whiteboard
A few interactive whiteboards can automatically detect projected images during a different type of calibration. The technology was developed by Mitsubishi Electric Research Laboratories Inc and is disclosed in patent 7,001,023. The computer projects a Gray Code sequence of white and black bars on the touch surface and light sensitive sensors behind the touch surface detect the light passing through the touch surface. This sequence allows the computer to align the touch surface with the display; however, it has the disadvantage of having tiny fiber-sized "dead spots" in the resistive touch surface where the light sensors are present. The "dead spots" are so small that touches in that area are still presented to the computer properly.