 IMCA mechanical calculator Version Française WikipédiA An italian calculator designed around 1958.

Inside
 This calculator can perform the four basic operations : Operands with 10 digits. Accumulator with 13 digits. Quotient with 8 digits. Second factor, when multiplying, with 8 digits. Copy back from accumulator to Operand. Bell ring when overflow. Cleaning the machine.

Operation
 To input an operand, use the cursors B, the number appears in A. The lever L sets the operand to zero. The lever K adds or substracts (according to the rotation) the operand in A to the accumulator in C. Each rotation is counted in D, the counter. Its digits are white for additions and red for substractions. The lever E set the counter back to zero and, if F is in the low position, it also resets the accumulator C. The accumulator C can be switched left or right compared with A to sum directly on tens, hundreds, etc. The lever I/J switches the carrier one position left or right. For a free and fast move, use the lever H. To copy C back to A, lower G (and F) and use the lever E to clear the accumulator as you copy it to A. Then, don't forget to raise G with a small pin on the right side to free every other movement. The cursors M are free and you can use them to set the comma. Add and Substract

Let's calculate 1524 + 97

 Note Actions Operand A/B Counter D Accumulator C Clear all F- E L `0000000000` `00000000` `0000000000000` Set first number and add it to the accumulator B=1524 K+ `0000001524` `00000001` `0000000001524` Set second number and add it! L B=97 K+ `0000000097` `00000002` `0000000001621`

Then 1524 + 97 = 1621

Let's calculate 20.14-19.66

 Note Actions Operand A/B Counter D Accumulator C Clear all, comma to second digit F- E L M2 `0000000000` `00000000` `0000000000000` Set first number and add it to the accumulator B=2014 K+ `0000002014` `00000001` `0000000002014` Set second number and substract it! L B=1966 K- `0000001966` `00000000` `0000000000048`

Then 20.14 - 1966 = 0.48

Multiply and Divide

How many hours in a year? 365 * 24

 Note Actions Operand A/B Counter D Accumulator C Clear all F- E L `0000000000` `00000000` `0000000000000` Set first number and add it 4 times to the accumulator B=365 K+ K+ K+ K+ `0000000365` `00000004` `0000000001460` Shift right to the tens, and add the number twice to the accumulator I K+ K+ `0000000365` `00000024` `0000000008760`

Then, there are 8760 hours in one year.

Sums and differences of products (314 * 12) + (15 * 24) - (47 * 31)

It's easy, each product is computed with the previous method, but, between them, you just clear the counter and not the accumulator! (Position F+ when using the lever E). The effect is that they are simply added!
If you want to substract, just rotate the other way with K-.

Approximate PI with the quotient 22 / 7 with three decimals.

The result will appear in Counter D, it's the number of turns that gives the quotient!

 Note Actions Operand A/B Counter D Accumulator C Clear all, comma to third digit for C and D F- E L M3 `0000000000` `00000000` `0000000000000` Set first number, shift carrier 3 positions to the right, add it to the accumulator B=22 I I I K+ `0000000022` `00001000` `0000000022000` Reset counter and set the divisor F+ E B=7 `0000000007` `00000000` `0000000022000` Substract 7 from 22 as many times as possible (*), shift left one digit K- K- K- J `0000000007` `00003000` `0000000001000` Substract 7 from 10 as many times as possible, shift left one digit K- J `0000000007` `00003100` `0000000000300` Substract 7 from 30 as many times as possible, shift left one digit K- K- K- K- J `0000000007` `00003140` `0000000000020` Substract 7 from 20 as many times as possible, shift left one digit K- K- J `0000000007` `00003142` `0000000000006`

Then PI is close to 3.142

(*) Note : if you substract too many times, then you hear a bell ring indicating an overflow. Then, just turn it back with K+, you'll hear another bell ring!

Square root

Let's calculate the square root of 215.4

You have to cut this number in blocks of two digits starting from the comma (because 100 = 10²):
`02 15.40`
We'll start working on the first block, the 2. On my IMCA, to get a good precision, place the carrier to have the arrow pointing at the 7th digit in the counter D. The, we'll get 6 or 7 digits for the square root acording to the number of digits in the first block.

This method uses the fact that the sum of the odd numbers is a square (1+3+5=9=3² for example). More details and theory here.

 Note Actions Operand A/B Counter D Accumulator C Clear all, columns B7-B4 we program the value and send it to the accumulatorr F- E L M3 B=2154 K+ `0002154000` `01000000` `2154000000000` Clear the counter, column of the first block (B7) start with 1 F+ E L B=1 `0001000000` `00000000` `2154000000000` Substract the odd numbers in serie until a bell ring, then turn back once, decrement B and move carrier left! B=1 K- B=3 K- ♪ K+ ♪ B=2 J `0002000000` `01000000` `1154000000000` Columns B7-B6 program the next odd number, 21, Substract the odd numbers in serie until a bell ring, then turn back once, decrement B and move carrier left! B=21 K- B=23 K- B=25 K- B=27 K- B=29 K- ♪ K+ ♪ B=28 J `0002800000` `01400000` `0194000000000` Columns B7-B5 program the next odd number, 281, Substract the odd numbers in serie until a bell ring, then turn back once, decrement B and move carrier left! B=281 K- B=283 K- B=285 K- B=287 K- B=289 K- B=291 K- B=293 K- ♪ K+ ♪ B=292 J `0002920000` `01460000` `0022400000000`
Then we would go on, columns B7-B4, with the odd value B=2921...

Then, the square root of 215.4 is close to 14.6

Depuis le 15 décembre 2007 