Since early history, mankind has devised means to help people learn in ways that are easier, faster, surer, or less expensive than previous means.[5][6] From this perspective, educational technology can be traced back to the emergence of very early tools, such as paintings on cave walls. However, the use of media for instructional purposes is generally traced back to the first decade of the 20th century,[7] with the introduction of educational films (1900's) and Sidney Pressey's mechanical teaching machines (1920's). The first large scale use of technologies may be training of soldiers in WWII by films and other mediated materials. The concept of hypertext is traced to Bush's description of memex in 1945.