Analog and digital 

The history of computing is divided into two major categories: digital mechanical calculators, carrying out only the four operations, and the analog computers which carry out all the functions of a modern scientific calculator except for the addition and subtraction. In analog mode the operations are the result of a sum of measurements and the numerical quantities are represented by means of continuous physical quantities (scales). It works simulating "by analogy" the operation to be performed. To clarify: if I put 10 stones of 100 grams each on the balance I will read 1 kg; if I add other 10 I will read 2 kilos, as long as the scale is accurate and if I am able to read it properly. properly scale. Two kilos are equivalent to 20 stones: I performed 10 + 10 in an analog way. With the digital system the numbers are represented by single units, such as the bead of the abacus or a number: 
counting the same stones I will have first 10 and doubling them 20. I have calculated digitally and the result is independent of the accuracy of the balance and the uniformity of the weights. It is impossible to make mistakes. 
The anemometer on the left shows the same data represented in both ways. The needle measures a distance and is less easy to read than the digital information, but it is more intuitive to notice the measured quantity. It must be remembered that 15.9 m / s indicates a strong wind, but the position of the needle over half scale tells us the situation immediately. For this reason the speedometers of the cars are always of the traditional type. 
Because the difficulty of reading the results seems inconvenient to use the analog system, but the logarithms permits to perform complex operations only marking them in form of scales. With the abacus, and later with mechanical calculators, you can perform only addition and subtraction. Multiply or extract roots in digital mode requires a long and tedious calculations. On the left the detail of a calculator for the iPod, that combines the immediate understanding of analog data with the precision of digital reading. 
The computer, derivative of mechanical calculators, has an history of its own that goes beyond this program but it should be remembered that the binary system was invented by Leibniz in 1679 just thinking to its use in a super computer and the first programmable machine, with punch cards, was built in 1801 by Jacquard for the production of fabrics. This system was then resumed by the first mechanical computer and then used until the 70s of the last century. Modern technology has ancient roots. 

Reading the display 
In the digital display the result is immediately understandable while in the analog one is a measurement and must be interpreted. Below the number 1,035,000 is expressed clearly and also with the abacus there are no doubts. Let's look at the same number on the slide rule: the reading is inaccurate but the engineers had such a good practice that errors hardly exceeded 2%. It was necessary to approximate, of course in excess, and the objects of the past were very robust creating the myth of the "Olde Good Things". 

In digital the result is easy to read ... 

1,035,000: even with the abacus can not go wrong 

1.035.000 on the slide rule can hardly be seen. 

... and also watching carefully is very difficult to read 

Nicola Marras 2008 
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