the number 1

Pythagorus believed that "Every thing in the world is made of units or whole numbers"
even music -> where the perfect harmonics tones sound much better than other. Higher harmonics are just combination of 2 or more harmonics. The lowest unit was 1. But later when worked on triangles he realised that his hypothesis was not true.

Arithmetic and Writing
In ancient time man started marking a line for 1. but he did not know how to count for a long time. Then instead of marking they started to keep a conical shaped clay piece. Every piece represents One of something. The use of conical piece was the invention of Arithmetic. Now people have some ones or many ones. When they exchange these pieces it either results in an addition or subtraction operation. Sometimes they used to keep these pieces in a bigger pot to remember the count of something. They also make the equal number of impression from the outside so as to know how many pieces are inside. Then someone realised that the pieces are not required. If they make impression on some sheet for each count it will serve the purpose. This leads to first CA, who keeps the record of things in a book. This also invented WRITING.

Other Numbers
When humans started living in the society, they required to distribute the food and other materials. This made them to invent other number. The first civilization to start using the bigger number were form India. They invented the symbols for 1 -9, which unfortunately are known as Arabic numbers.

From Counting to measuring
To build road and building, we require exact measurement. The need to exactly measure the lenght leads to the invention of ruler. First ruler was equal to the length of arm of some person. Replicas of such ruler were made and used for construction purpose. The first rules was used by Egyptians.

The Zero
The first written document of zero could be found on the wall of a temple in Gwalior. It dates back to 11Th BC. Indians not only invented zero, they invented the digit numbers. By combining different numbers Indians were able to write any number, no matter how big or small was it.
This gave the Indian astrologers edge over the others. They are the first to discover that earth revolves on its axis, and it moves around the sun much before Copernicus. They also calculated the diameter of earth (with only 1% variation).

The number system moves from India to middle east (Iraq). The Muslim law system requires a better number system as many of its law requires to precisely calculate the share. The middle east took the match to new heights with the discovery of algebra, quadratic equation, logarithms...

Indian Numeral Vs Romans
The roman numerals were used by all the Europe as it was under roman control. The other side of Mediterranean sea was using Indian numbers. Fibonacci learned the India numerals from middle east and took them to Europe. It took some time for the Europeans to start using Indian system as they found it little difficult. Also the number ZERO was not clear and was looked with suspicion. They used to call it Cifar. The word Cypher (meaning suspicious) originates it roots from this. But the Indian number system proved much better in calculating exact values especially the interest. With the Capitalism on advance, India system was excepted.

The Binary Numbers
In 16th century, Leibeintz wanted to build a mechanical calculator to get rid of the human error. He realized that we really don't need 10 different numerals to count. All we need is only 1 and 0. He build a binary mechanical calculator. Although he didn't worked much on that. It was only in 1944 that the first calculating m/c was built on binary system. Only this time it was electronic m/c.