jan 1, 1960 - By the 1960s, overhead projectors were commonly used in schools.

Description:

By mailer_diablo (Self-taken (Unmodified)) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Added to timeline:

Date:

Images: