calculator’s keypad.

Not only calculator apart from mobile phones all machines have reversed numbers. Look your pc or laptop too. Calculator or other calculating machines number established like this because these numbers like 7,8,9 are most commonly used for calculating a big amount it's easy to use. Phone number keypad start from bottom to top because in starting phone makers doesn't want to jam their lines so they established a bit typical keypad which we still used today.

I too think when u raise this question. I u got answer share