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 in modern TI calculators is denoted by a lower case "a" at the end of the model number (e.g. TI-30a). In older models, such as the TI-36 Solar, "Anylite Solar" is printed on the calculator. As of the 2010s, some very cheap calculators include a "dummy" solar panel, implying that they are solar-powered, when they are actually powered only by battery. 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