If you have noticed the keypad on your phones and calculators carefully, you will notice that while phones have 1-2-3 in the top row, calculators have 7-8-9. What is the reason behind this? Is there any particular advantage? Or any psychological reason? Read on to check the reason.
1. In the early 1900s, rotary telephones came to the USA.
The phones had numbers 1 to 9 sequentially, while 0 was placed after 9.
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2. Keypad phones came in the 60s.
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3. Push-button phones were still not available to the public.
During that time, several studies were done to find out which number layout minimises chances of error while dialing. 
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4. According to Journal of Applied Psychology
People usually arrange letters as well as numbers in the same order they read.
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5. So many combinations
Companies found out that there were 9^9 possible combinations, which is equal to 387420489. That is huge!
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6. But logical ones are less
Although the number of combinations is mind bogglingly huge, that doesn’t mean you will dial all of them, so they tested only the logical ones.
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7. Bell Labs conducted a study in 1960s
They found out that most people preferred a horizontal placement of two rows of buttons. This design minimized errors and was also the fastest.
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8. Texas Instruments created its first handheld calculator prototype in 1967.
The top row had the numbers 7-8-9. They followed this method since earlier desktop adding machines followed the same pattern.
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9. At present, calculators and phones have two separate keyboard layouts and people have become used to them.
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