The Arabs used letters to denote numbers, and perhaps they took this idea from the Greeks, the Nabateans, or the Aramaeans, and it is as follows:
This is called the eastern Arabic alphabet.
If the Arabic computer has written:
If it is preceded by a smaller letter, it is a repetition.
As for this numbering, it is like the Greek numbering that indicates numbers only and does not help in performing arithmetic operations because it is easier for the computer to realize that 500 + 200 = 700 than it is to realize that ث + ر= ذ .
The Arabic alphabetic numbering is distinguished from the Egyptian and Babylonian numbering in that it is more abbreviated and does not need to write the repetition numbers, but as the Egyptian numbering, it is not decimal places, so astrologers used a numbering in which the abbreviation as the Arabic alphabetic numbering and the decimal places of the Babylonian numbering.
*** This numbering is found in the Arabic astronomical books, but this numbering was avoided by the public and they did not use it, but they used a method of calculations called the hand account. This calculation depends on the shapes of the hand agreed upon to indicate the different numbers.