Programmable calculator to use magnetic strips were the HP-41C and TI-59. Continuous memory does not lose its content when the calculator is switched off. With continuous memory the user can, for example, change batteries without losing the entered programs. Compact Cassettes offered a simple, inexpensive alternative to magnetic cards. Usually, an interface module, such as the Casio FA-1, was used to connect the calculator to an ordinary cassette recorder and digital data were encoded as frequency-shift keyed audio signals. Sharp and Hewlett-Packard also sold dedicated micro- or mini-cassette recorders that connected directly to the calculator. These set-ups, while being more practical and
APF Electronics Inc. math learning tool and standard calculator, but it has 6 different overlays that convert it into one of several games. APF Imagination Machine II was a computer-video game console hybrid that was in the final development stages around 1983. It was more powerful and was an all in one unit. The project was canceled. It is unknown if any prototypes exist. The North American video game crash of 1983 caused the project to be canceled and APF, then a publicly traded company, filed for bankruptcy. APF Electronics Inc. APF Electronics, Inc. was a publicly traded company in the United States