A brief history of the numeric keypad

There’s no logical reason why telephones and calculators use different numeric keypads. So why do we still follow the same convention?

Picture the keypad of a telephone and calculator side by side. Can you see the subtle difference between the two without resorting to your smartphone? Don’t worry if you can’t recall the design. Most of us are so used to accepting the common interfaces that we tend to overlook the calculator’s inverted key sequence. A calculator has the 7–8–9 buttons at the top whereas a phone uses the 1–2–3 format.

Telephone (left) and calculator (right) keypads

Subtle, but puzzling since they serve the same functional goal — input numbers. There’s no logical reason for the inversion if a user operates the interface in the same way. Common sense suggests the reason should be technological constraints. Maybe it’s due to a patent battle between the inventors. Some people may theorize it’s ergonomics.

With no clear explanation, I knew history and the evolution of these devices would provide the answer. Which device was invented first? Which keypad influenced the other? Most importantly, who invented the keypad in the first place?

Typewriters, Cash Registers, and Calculators

Looking at the key arrangement, I was curious to learn when the system of using keys was introduced in the history of machines. The keyboard came about sometime between the first and second industrial revolutions (from 1820 to 1920). Some inventors had already begun experimenting with machines similar to pianos in the late 18th century.

However, it wasn’t until 1844 that a Frenchman by the name of Jean-Baptiste Schwilguć came up with the first working prototype of a key-driven calculator machine. This machine used the first numerical keyboard with a single row of keys that increased from 1 to 9 (Dalakov, 2018).

In all fairness, though, we have to mention two predecessors that could claim they invented the key-based interface. In 1834, Luigi Torchi reportedly showed a prototype of a wooden calculator, with a design similar to the typewriter. In 1822, author James White’s New Century of Inventions showed a key-based device with nine numeric keys. Neither one stood up to the test of time, nor no proof was given that they weren’t just fantasy (Durant, 2011).

Jean-Baptiste Schwilguć’s adding machine keyboard (1844)

Still, White’s machine, even if it was a proof of concept, could certainly be regarded as the earliest example of modern “direct-manipulation” interface. This interface that allows users to focus on the input without the need to operate the bare mechanisms such as the Pascaline or array of Arithmometers that use drums, clocks and unfriendly levers (Dalakov, 2018).

However, these “ideas” still don’t provide an explanation as to why modern calculators use the reverse 9–0 arrangement.

Theories include the suggestion that the calculator was based on the cash register design. Think about it, the currencies used in that time meant the number 0 was often the most pressed key. So, it would make sense to keep that number at the very bottom to ensure it was within hand’s reach (Durant, 2011).

While there is some truth to the explanation, it’s still riddled with factual errors and the hand’s reach argument was weak. This is especially so since early cash registers (until 1893) had no separate 0 key, no drawer and no workers standing behind the cash register.

For the argument to be valid, it’s important to look at the birth of cash registers.

In 1879, James Ritty owned a saloon in Dayton, Ohio where he found some of his employees were stealing his profits. After seeing a tool that counted the revolutions of a steamboat’s propeller, he invented the machine that featured a clock-wise device and a set of numeric keys (Dalakov, 2018). The predecessor to today’s cash register was not meant for calculation but to record a sale and let a manager know with a ring.

Until 1893, the early register models had buttons commonly arranged in one or two horizontal rows, which displayed preset values — 10, 15, 20, 30, 35, etc. These corresponded to the price, in cents, of items sold in stores and saloons. The introduction of the three vertical rows of digits didn’t happen until 1894 when the NCR Model 79 became available.