Since the late-1980s, simple calculators have been installed in other small devices, such as mobile phones, pagers or wrist watches. It might also have a Cancel Entry button, to clear the current numbers being entered. More advanced models may have a single-number memory, which can be recalled where necessary.Other basic functions, such as square root and percentage (%).A Cancel (or clear) button, to clear the current calculation.The four arithmetic functions (namely, addition, subtraction, multiplication and division).The equals sign, to prompt for the answer.A display, usually made from LED lights or liquid crystal (LCD), capable of showing a number of digits (typically 8 or 10).A power source, such as a battery or a solar panel or both.A simple modern calculator might consist of the following parts: The complexity of calculators varies with the intended purpose. Today, most calculators are handheld microelectronic devices. The first mechanical calculators were mechanical desktop devices which were replaced by electromechanical desktop calculators, and then by electronic devices using first thermionic valves, then transistors, then hard-wired integrated circuit logic.

In the past, some calculators were as large as today's computers. Modern calculators are electrically powered and come in countless shapes and sizes varying from cheap, give-away, credit-card sized models to more sturdy adding machine-like models with built-in printers. This semi-manual process of calculation was tedious and error-prone.

The word 'calculator' denoted a person who did such work for a living using such aids as well as pen and paper. In the past, mechanical clerical aids such as abaci, comptometers, Napier's bones, books of mathematical tables, slide rules, or mechanical adding machines were used for numeric work.

6.4.2 The development of electronic calculators.

6.4.1 Mechanical calculators reach their zenith.

Friden calculator circa 1960