Milestones in the History of Calculators

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After Sharp launched its first thin scientific calculator equipped with liquid crystal display (LCD) in 1977, several new models were introduced: EL-5806's 8 + 2-digit display capacity not only outpaced other Sharp LCD models, but similar types of competitors.

By 1979, the EL-5806S with similar capabilities and the new EL-506 were completed. Latter has display capacity of 10 or 8+2 digits, depending on the display mode, and can handle area functions (arc hyp) too. It was replaced in 1981 by the EL-506S, which has undergone a minimal cosmetic change with the same knowledge. EL-506H was introduced the same year, and became a long-time hit: it was manufactured until 1989 at the Chinese subsidiary of Sharp Corporation. Its design is extremely simplified, with a single-sided printed circuit board containing only one potentiometer in addition to the chip and the display. EL-506H introduced displaying and calculation with hexadecimal numbers.

In 1984, a new member of the series, the more advanced EL-506P was introduced. It was able to convert angles given in different units, numbers between binary, octal, decimal and hexadecimal notations, and handle complex numbers. In the early series, it contains a new flexible printed circuit board directly connected to the display and keyboard, and a year later it was replaced by a special packaged IC manufactured by Toshiba, which eliminated the need for a printed circuit board.

With the replicas of the chip used in EL-506P, the first „clones” was built in similar housing as used in EL-506H, at various factories in Hong Kong, Taiwan and China. Later, with similar appearance and same model number, a simple programmable calculators based on a genuine Sharp chip — which was made for Sanyo — completed. The story and types of clones and fakes will be discussed in a separate article.

In 1986, EL-506A and its equivalent, the EL-556 was introduced, which had 10 + 2-digit capacity, two independent memory registers, engineering display mode, and was capable of combinatorial calculations, logical operations, and can solve 3-variable equations. In its design, the same process can be seen as for its predecessor, the EL-506P: first it was made with a flexible PCB and later with a specially packaged chip.

The next member in the series, the EL-506D (and the EL-556D), appeared in 1990. The manufacturing lines was moved to Taiwan and Thailand, and due to cost-effectiveness, new plastic housing was designed, and cheap two-sided PCBs was used. These machines could not be disassembled, repairs are almost impossible. The novelty of the D series was the dot matrix portion on the left side of the display, which was able to display the last pending operation and other information during the calculations. It has built-in storage for constants and conversion factors, and has been extended with integral calculation and six kinds of regression modes.

In 1992, the first 506 model with formula-interpreting technique (DAL = Direct Algebraic Logic) was introduced. The new EL-506G (EL-556G) can acquire formulas in the same was as written on paper. The last pending operation was also shown on the left side of the display (called Function Display), and it was absolutely necessary, because unlike later types, we could not see and edit the entire operation sequence so far. Calculation of integrals was abandoned, but possibility of random number generation and fractional calculations appeared.

The Advanced DAL Series which was introduced in 1996, has the EL-506L (EL-556L) member with two line display, which allow to correct or rewrite the entire entered formula at any time, even after performing a calculation (Playback function). There was no change in its functions, only the technology was replaced with cheaper alternatives: the chip was mounted on two-sided PCB, but the keyboard has a second, one-sided PCB connected with foil cables.

In 1999, with the introducing the new R-series, the EL-556 was discontinued, and replaced by the EL-546R, which, like the previous 546s, had solar cells and many other functions: calculating integrals and with stored user-defined formulas. The EL-506R was identical to the EL-546R. In 2002, this type was replaced by the new V-series models (EL-506V, EL-546V) in a new color and form, but with the same knowledge.

In 2005, the EL-506W (EL-546W) was introduced as a member of the W series. New features in the W series include advanced menu functions and extended 14 + 2-digit internal capacity.