Calculating - Addipresto
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Olivetti 15 £sd
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For an explanation of £sd money
see the Money page
 
 
 
 
 
Addipresto
Model    
Maker   Brevetti Lanza
Origin   Italy
Date   1950s
Serial    
 
A neat desk-top adding machine. A stylus is used to pull down on the bands. The band is pulled right to the bottom causing the total in the window above to change. Only adding is possible.
 
The red lever on the left clears the display to zero. The stylus would have been placed in the hole on top when not in use. Mine is missing and marks on the number bands suggest a pen was used. This would have been better for the operator who would need to write down the results.
 
Care must be taken as it is possible to pull the bands too far and cause a 9 to be added as 10.
 
 
Addipresto
Model    
Maker   Brevetti Lanza-Savona
Origin   Italy
Date   1960s
Serial    
 
This is a decimal version and is complete with box, cover, stylus and instructions. Subtraction is possible using a number's complement. The advert and the instructions show this model was ready for use with decimal money introduced in 1971.
 
 
The complement of a number (on this machine) is the difference between that number and 9. Using this system, the complement is added to the value in each column, including any column with a zero. However, to finish the calculation, a 1 has to be added to the result.
 
This could have been avoided if the right-hand column had been marked with complements of 10 instead of 9, with zero treated as 10.
 
The complements would have looked like this:
 
0 9   0 9   0 9   0 9   0 9   0 9   1 9
1 8   1 8   1 8   1 8   1 8   1 8   2 8
2 7   2 7   2 7   2 7   2 7   2 7   3 7
3 6   3 6   3 6   3 6   3 6   3 6   4 6
4 5   4 5   4 5   4 5   4 5   4 5   5 5
5 4   5 4   5 4   5 4   5 4   5 4   6 4
6 3   6 3   6 3   6 3   6 3   6 3   7 3
7 2   7 2   7 2   7 2   7 2   7 2   8 2
8 1   8 1   8 1   8 1   8 1   8 1   9 1
9   9   9   9   9   9   0
 
Using the revised table above, to deduct 345 from 975 we would add the red figures 9999345 where the carry will result in the answer 0000630.
 
Another way of looking at complements is to see the complement of any number, of any number of digits, as the difference between the number and 10 to the power of the number of digits.
 
The complement of 4 is therefore 10 - 4 or 6, the complement of 44 is 100 - 44 or 56, the complement of 1234 is 10000 - 1234 or 8766. You will see that these match the revised table.
 
The complement of 0000345 (padded with zeroes because we have a seven column adding machine) is 1000 - 345 or 0000655, the values in black alongside the red 9999345 used above.
 
 
 
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