A keypad is a set of buttons arranged in a block or "pad" which usually bear digits, symbols and usually a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad. Keypads are found on many alphanumeric keyboards and on other devices such as calculators, push-button telephones, combination locks, and digital door locks, which require mainly numeric input.

## Invention

The invention of the keypad is attributed to John E. Kerlin, an industrial psychologist at Bell Labs in Murray Hill.[1]

## Uses and functions

A computer keyboard usually has a small numeric keypad on the side, in addition to the other number keys on the top, but with a calculator-style arrangement of buttons that allow more efficient entry of numerical data. This number pad (commonly abbreviated to "numpad") is usually positioned on the right side of the keyboard because most people are right-handed.

Many laptop computers have special function keys which turn part of the alphabetical keyboard into a numerical keypad as there is insufficient space to allow a separate keypad to be built into the laptop's chassis. Separate external plug-in keypads can be purchased.

As a general rule, the keys on calculator-style keypads are arranged such that 123 is on the bottom row, whereas in a telephone keypad, there will be the 123-keys at the top. A phone key-pad also has the special buttons labelled * (star) and # (octothorpe, number sign, "pound", "hex" or "hash") on either side of the zero key. Most of the keys on a telephone also bear letters which have had several auxiliary uses, such as remembering area codes or whole telephone numbers.

The keypad of a calculator contains the digits 0 through 9, from bottom upwards, together with the four arithmetic operations, the decimal point and other more advanced mathematical functions.

The reason that the keypad of keyboards and calculators are different is the subject of some uncertainty. There are several popular theories and folk histories. One popular theory suggests that the reason is similar to that given for the QWERTY layout, the unfamiliar ordering slowed down users to accommodate the slow switches of the late 1950s and early 1960s.[2] Although calculator keypads predate telephone keypads, telephone designers had several reasons to use the descending order. At the time of the introduction of the telephone keypad, telephone numbers in the U.S. where commonly given out using alphabetical characters for the first two digits. Thus 555-1234 would be given out as KL5-1234. These alpha sequences were mapped to words. "27" was given out as "CRestview", "26" as "ATwood", etc. By placing the "1" key in the upper left, the alphabet was arranged in the normal left-to-right descending order for English characters. Additionally, on a rotary telephone the "1" hole was at the top, albeit at the top right. Finally, some sources state that AT&T conducted research to see which ordering resulted in the least confusion.[3]

The definitive answer appears to be the result of a research study conducted by Bell Labs published in 1960: "Human Factor Engineering Studies of the Design and Use of Pushbutton Telephone Sets" by R. L. Deininger.[4] This study concluded that the adopted layout was best.

Keypads are also a feature of some combination locks. This type of lock is often used on doors, such as that found at the main entrance to some offices.