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
Solar-powered calculator Solar-powered calculator Solar-powered calculators are hand-held electronic calculators powered by solar cells mounted on the device. They were introduced at the end of the 1970s. Amorphous silicon has been used as a photovoltaic solar cell material for devices which require very little power, such as pocket calculators, because their lower performance compared to conventional crystalline silicon solar cells is more than offset by their lower cost and simplified deposition onto a substrate. The first solar powered calculators available in the late 1970s included the Royal "Solar 1", the Sharp "EL-8026", and the Teal "Photon". Solar calculators use liquid crystal displays