The original ten key was an adding machine. The three by three arrangement of keys was first used in 1911 on a machine invented by David Sundstrand of the Sundstrand Adding Machine Company. Similar machines are still used by accountants and other professionals who do a lot of mathematics. Instead of using an "=" key to complete an equation, they usually have a key marked "T" for total, which serves the same purpose. These machines have become somewhat less common as computers have become more popular, but are still useful in some professions. Calculators often feature a similar number pad layout, but typically offer many additional keys to handle more complicated mathematics.
A ten-key layout is commonly found on personal computer keyboards, usually to the right of the alphabet keys. Laptops and other small computers may only offer number keys above the main keyboard or include a number pad that shares keys with letters on the right side, as a separate keypad takes up too much space. Left-side keypads are available, although they are uncommon; in addition, separate USB ten keys can be plugged into a laptop or other machine. Most computers, even those without a separate number pad, usually have a ten-key calculator accessory that displays on the screen.
The telephone key board is upside down from the adding machine and computer. Why that happened? Many theories have been trying to explain, but it remains uncertain. However, the first theory deals with the telephone's circuitry and tone-recognition hardware. When the touch-tone telephone was being designed in the late 1950s, the calculator and adding-machine designers had already established a layout that had 7, 8 and 9 across the top row. Data-entry professionals, and others who used calculators regularly, were quite adept at navigating these keypads. They could hit the numbers extremely quickly, which was great for data entry, but not so great for dialing a touch-tone phone. The tone-recognition technology could not operate effectively at the speeds at which these specialists could dial the numbers. The telephone designers figured that if they reversed the layout, the dialing speeds would decrease and the tone-recognition would be able to do its job more reliably. This theory has little proof to substantiate it, but it does make sense.
https://en.wikipedia.org/wiki/Mechanical_calculator. Acessed in 10/20/2017
http://www.wisegeek.org/what-is-a-ten-key.htm. Acessed in 10/20/2017.
"About 1950 in the family wholesale grocery, we bought a new electric Ten Key adding machine to add the invoices for delivery every morning.
Included was exercises to learn the ten key by touch. Our operator said she didn't need the exercises and she wouldn't look at the adding machine anyway. Some of us would stand behind her for a while and just observe. Of course her head would swing back and forth and yours does too.
In the course of time, after practicing the exercises few minutes per day, she could operate the adding machine without looking at it. It increased her speed typing the numbers and most important, it increased her self-confidence.
If you will practice these exercises each day for a few days, you may be as quick and accurate as I am (This was written years ago).
TIP: When proofing a column of figures, always subtract the total. you will have a zero balance. It prevents you reading the balance as what you know it should be rather than what it is.
Never look at your adding machine again. I have often added a list of numbers, looked for the total and found that I didn’t have the adding machine turned on.
Multiplication is repeat addition. Division is repeat subtraction.
To multiply 7 x 8 on the old adding machines you had to index or hold down the number 8 key and pull the handle or cycle the motor 7 times.
For a long time many banks preferred the Full Keyboard Machine to Ten Key Machine because when missed indexing a key, it would cause a large error. But almost everything has an outside proof.
I have always thought you would know if you made a mistake if you were operating the Ten Key by Touch.