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The Corema Portative is a relatively small and lightweight full keyboard calculator. It was made by Corema S.A. in Geneva, Switzerland. It was also sold under other names, for example in Germany it was sold as Simeca, and in the USA as Corexa.

This calculator has an 8-digit register at the top, covered by a rectangular plastic lens that magnifies it for easier reading. The keyboard is a bit like a Comptometer, with 8 columns each containing nine keys from 1 to 9. A transparent overlay sheet on the keyboard shows vertical white lines that separate the key columns in groups of 3+3+2 (e.g. for money calculations involving cents), or you can turn over the sheet to separate them in groups as 2+3+3.

There is a large button on a lever at the front right, and while it would seem like you'd need to press that lever to perform each addition or subtraction, it is not quite so clear cut which makes this a rather confusing machine to operate. There is a full description of how to use the machine below. To the right of the keyboard are four buttons, marked 0 (to clear the register), C (for corrections), - (to subtract) and = (to give the result of a subtraction). Above these is the repeater dial, a small dial which can be set to positions marked A, the digits 2 to 9, or R.

The Corema Portative was designed by Chi Liang Cho, and was first made in 1945. This version did not have the repeater dial. The MC15 with the dial was made from around 1952 or so, but I do not know when production ended or how many were made. The serial number on my machine is 23128.

The machine comes with its own small suitcase box, for storage and transport. The large plunger button has to be rotated inwards to allow it to fit inside the box. It seems that this button can break off when not handled properly, and mine has been broken and glued at some point in the past.

Here is a video where I demonstrate the Corema Portative MC15.

The French instruction booklet that came with my machine is in poor condition, but seems to be complete. You can download a scanned version of it (PDF, 3.77 MB). Note that the diagram on the first page of that file actually folds out from the rear page of the manual so that it can be kept visible while reading the text.

Here is my own short set of instructions. On most other machines that have a big lever like this one, the lever is pushed to actually perform the addition/subtraction operation. The oddity of this machine is that the lever is mostly pushed beforehand to prime the mechanism, and the operation is then done as you push the buttons on the keyboard.

**Preparing for use:** Pull apart the lever and its button so that the
button can be rotated until it points forward. Then push down the lever
fully so that it springs back up. Fold out the two legs at the rear to
tilt the machine towards you.
**Preparing for storage:** Press the C button to lock the keyboard.
Fold in the legs (push them sideways towards each other to
unlock them and then fold them down). Pull apart the lever and its button
so that the button can be rotated until it points backwards towards the
keyboard. Then push down the lever as far as the twisted button allows.

**Addition:** Set the repeater dial to A (for Addition). Push down the lever
to prime the mechanism. Type the number you want to add, and each digit you type
is immediately added to the register. The typed keys remain depressed. To add another
number, push down the lever (which also clears the keyboard) and type the next number.

**Clearing:** To clear the register, press the button marked 0. Push the
lever to prime the mechanism before you can start your next calculation.

**Correction:** If you have entered the wrong number, press C. The
entered number is cleared, and the register reset to the value before
the number was entered. You will have to push the lever again to prime
the mechanism before you can enter the next number.

**Subtraction:** Set the repeater dial to A (just like addition). Push down the lever
to prime the mechanism. Press the button marked with a minus sign '-'. Type the
number you want to subtract. Note that unlike addition, the register does not yet
show the result as you type. When you have finished entering the number, press
the '=' key to display the result. This will also release the keys, but you will
have to push down the lever before you can do any further calculation. Note that
you cannot perform a correction after you have pressed the '=' key.

**Negative numbers:** If you subtract a large number from a smaller number,
the resulting negative number cannot be displayed normally as the register
will underflow. To work out what negative number is being displayed, you have
to find out what to add to make the register show zero, which can be done as
follows. Push down the lever to prime the mechanism. Starting from the right
column, look at the digit being displayed, and if it is non-zero, press
the button which when added makes it ten. Do this with each column in turn
from right to left until the register shows only zeroes. The pressed keys
in the keyboard now show the negation of the number that was displayed.

**Simple Multiplication:** Suppose you want to multiply a number by a
single digit. Push down the lever to prime the mechanism. Type the number
you want to multiply, and each digit you type is immediately added to the
register. Set the repeater dial to the digit you want to multiply the
entered number by. Repeatedly push down the lever. Each time you do so,
the entered number is added again to the register, and the repeater dial
is rotated to the next smaller digit. On the last addition the repeater
dial turns from 2 to A, so the next push on the lever will clear the keyboard
(and no longer change the register), ready for the next operation.

Instead of multiplying by a fixed single digit, you can set the
repeater dial to R (for Repeat). Enter a number, which gets added to
the register, and push down on the lever however many further times
you want the number to be added. When done, turn the repeater dial
back to A yourself, and push the lever to prepare for the next operation.

**Advanced multiplication:** Multiplication by a number of more than one
digit is done by splitting it into single-digit multiplications. For example,
suppose you want to multiply a number by 56. First multiply it by 6 as
described above, i.e. push the lever, enter the number and set the repeater
dial to 6, push the lever 5 more times to do the multiplication, and push
the lever once more to clear the keyboard. Now we have to do the multiplication
by the second digit. Enter the number on the keyboard again but shifted one
column to the left. Set the repeater dial to 5 (the next digit of the number
you want to multiply by), and pump the lever 4 more times to complete the
multiplication, and once more to clear the keyboard.

**Division:** As subtraction is mechanically done differently to addition,
it is not possible the use the repeater dial or the correction key with it.
It is therefore not possible on this machine to perform division as repeated
subtraction. A method was divised that uses repeated addition instead, with the
repeater dial set to R as described above. The example in the manual is 4476
divided by 12.

The result will be 3 digits long, so reserve the rightmost 3 columns
for it (i.e. columns 6, 7, 8 when numbered from left to right). The first
four columns (columns 1 to 4) will be used to build 4476 from multiples of
12.

Enter 12 in columns 1 and 2, and a 1 in column 6, so the register shows **1200**0**100**. Press the lever
repeatedly until the first two digits of the register exceed 44 (which
will be after 3 lever presses). Press the Cancel button to clear the
keyboard and undo the last addition. The register displays **3600**0**300**,
so the first digit of the answer is 3.

Enter 12 in columns 2 and 3, and a 1 in column 7, all one column to the right
sompared to the above. Press the lever repeatedly until the first three digits of
the register exceed 447 (which will be after 7 lever presses). Press the Cancel
button to clear the keyboard and undo the last addition. The register displays
**4440**0**370**, so the second digit of the answer is 7.

Enter 12 in columns 3 and 4, and a 1 in column 8. Press the lever
repeatedly until the first four digits of the register reach 4476 (which
will be after 2 lever presses). The register displays **4476**0**373**,
so the answer is that 4476/12 = 373.

The small article in the Journal de Geneve proves that the first version of the Corema
already appeared in 1945, four years earlier than most other sources claim, though it
may have taken a while before full production started.

I found a few ads in Dutch and Swiss newspaper archives, including personnel ads. The
1952 Swiss ad clearly shows a picture of the MC 15 though that model name is not used
in the text.

There is only one Swiss patent assigned to Corema S.A. that can be easily found in the European patent database, as well as two patents by Chi Liang Cho. There must be some more patents for aspects of this machine - for example in the manual even the transparent overlay for the column markings is said to be patented.

Patent | Filing date | Publish date | Name | Description |
---|---|---|---|---|

CH 263,699 | 10-09-1947 | 01-12-1949 | Corema S.A. | Keyboard locking mechanism |

CH 265,242 | 22-03-1944 | 30-11-1949 | Chi Liang Cho | Adding and subtracting machine
See also: CA 514,948, DE 903,999, DK 73,682 C, ES 173,808, FR 927,192, US 2,623,695. |

CH 272,863 | 28-03-1947 | 15-01-1951 | Chi Liang Cho | Multiplier digit |

- Rechner Lexikon has a page on the Corema MC 15. It also links to a scan of the German version of the manual, and a page on the first model Corema Portative.
- Rechenmaschinen illustrated has pictures of a Corema, missing its dial and lever button.

© Copyright 2018-2020 Jaap Scherphuis, mechcalc a t jaapsch d o t net.