The TI-30 is a scientific calculator manufactured by Texas Instruments, the first model of which was introduced in 1976. While the original TI-30 was discontinued in 1983 after several design revisions, TI maintains the TI-30 designation as a branding for its low and mid-range scientific calculators. Price The original TI-30 was notable for its very low cost for the time, around US$25. This was much less than the retail prices of other scientific calculators of the era; for example, Hewlett-Packard's cheapest scientific calculator at the time was still well over $100. The Casio FX-20, another popular scientific calculator, sold for roughly double the price of the TI-30. The TI-30 sold for less than the cost of a professional-grade slide rule. The TI-30 sold an estimated 15 million units during its lifespan from 1976–1983. Description The original TI-30, a cost-reduced but functionally equivalent version of TI's SR-40 unit, utilized an LED display, was powered by a 9-volt battery, and contained nearly all of its functionality in one chip, where previous calculators used many discrete components. The TI-30 could perform nearly all the logarithmic and trigonometric functions of an HP-21, its primary competition at the time. Although the Texas Instruments SR-50 pioneered algebraic notation with operation precedence in 1974, the TI-30 made those features available at a more affordable price. Early production TI-30 units (c. 1976) contained a logic error in their calculation of inverse tangents. On these early models, pressing "0 INV TAN" would cause the calculator to go into an infinite loop until it is powered off with the OFF button. The "0" had to be pressed on the keyboard; the calculator produced a correct answer if the "0" was the result of a previous calculation. The TI-30 was at one point the most popular scientific calculator for junior high and high school use in the United States. For $24.95, the purchaser received both the calculator and a 224-page book, , which covered basics in algebra, business and finance, trigonometry, probability and statistics, physics and chemistry, and had ideas for games and puzzles that could be played with the calculator. In 1980, Texas Instruments converted the TI-30 to use a liquid crystal display, releasing the TI-30 LCD in Europe and the TI-30 II a year later in the U.S. The calculator itself remained functionally similar over several redesigns in the following few years, with solar power coming to the line