A filmstrip cartridge for a teaching machine. This one contains training for deliverymen stocking Coca-Cola vending machines.

A Mast cartridge contains two filmstrips, each of which contains two topics. A topic consists of a series of a questions and answers. Each frame holds one step of each topic flipped vertically in the upper and lower halves of the frame. The topics run in opposite directions; when one topic is finished, flipping the cartridge positions it at the start of the second topic. The filmstrip is advanced by pressing the right-hand tab below the screen. When a new frame appears, the answer is hidden below the question. The frame cannot be advanced again until the user unblocks the answer by pressing the left-hand tab. The original patent (US Patent 3305942) also describes an optional paper tape for writing down answers, although that is not present in this example.

The Mast Development Co. was started by Gifford M. Mast in 1944. Mast had a Master of Science degree in engineering science from Harvard and taught physics at St. Ambrose College on Davenport, Iowa. Before the Second World War, he worked for Tru-Vue, receiving a patent (US Patent 2326718) that appears to be the 1947 version of the Tru-Vue stereoviewer. Although president of the Mast Development Co., he seems to have remained a hands-on inventor; he held numerous patents, including the one for the Mast Teaching Machine.

His interest in 3D continued and in 1963 Mast Development Co. acquired the Keystone View Co., once the world's largest publisher of stereoviews. Mast eventually donated Keystone's photo archives to the University of California Riverside, perhaps his most enduring legacy.