What was before calculator to calculate the numbers? The Slide Ruler was the one which was the mathematical tool for addition, multiplication, logarithmic and other calculations, a way back than computer was invented.
The Slide Ruler was first invented by William Oughtred in 1625 and the first pocket-sized scientific calculators was introduced by Hewlett Packard in 1972.
Follow the link to learn more about the history
http://trillian.randomstuff.org.uk/~stephen/history/timeline.html
http://en.wikipedia.org/wiki/Slide_rule
The Slide Ruler was first invented by William Oughtred in 1625 and the first pocket-sized scientific calculators was introduced by Hewlett Packard in 1972.
Follow the link to learn more about the history
http://trillian.randomstuff.org.uk/~stephen/history/timeline.html
http://en.wikipedia.org/wiki/Slide_rule