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This machine was manufactured by FACIT in Sweden, in 1951 (see here). I bought it at an online auction site, in April 2019, right after finding my NEA. As in that case, there was no way of knowing if the motor would run, since the seller only said it was completely jammed, and that he didn't have the power cable. In spite of three missing keys, I bought it anyway, for three times the price I paid for the NEA. The exterior was very attractive, displays were all zeroed, and the ADD key was slightly lower than its reset position, so I guessed the jam would be related to that.

This machine evolves from the NEA, replacing the two reset levers to the left with electrically-operated clearing mechanisms for all three registers. Also moving forward from the NEA's design, there is an automatic multiplying function, that also works for squaring. The division works exactly in the same way, also automatically. Thus, this model was the first FACIT to be fully automatic for the four operations.

My machine has octogonal keytops for the shift functions, and a knurled lever for the stop/sub function. This lever was replaced with a regular button in later models, and the TK-style octogonal keytops also evolved into rectangular ones. My machine also lacks the secondary control lever, to the right of the main control (must-add-div) lever. This is strange, since the NEA has this lever, and its bottom prints symbols to remind the operator of its function. Most other pictures of ESA-0 machines I found online also have the secondary lever. So far, I could not find an explanation for this; there is no indication that the lever was removed or broken.

Putting it back to work was a demanding process, since initially the motor ran continuously, and all other mechanisms were locked. It took some analysis, observation, kerosene jets and lubrication to unlock the typical parts of the FACITs that cause the most important locks. After two careful days, I built it a new power cable, then I managed to stop the motor, make the clearing mechanisms work, unlock the main rotor, release the locks that kept me from entering numbers, activate the adding mechanism, and finally to multiplications and divisions. It now works perfectly. Next step: 3D print the missing keytops, and replace the rubber rollers at the back – as 12 kilos, this was the first FACIT machine to have rollers to help moving it around an office desk.

Multiplication in the ESA-0 is automatic: the operator types in the multiplicator, presses the X button. This places the multiplicator in a “mechanical memory” of sorts, and the display remains zeroed. Then the operator inputs the multiplicand, and presses the = key. The result comes out automatically, with all rotor rotations and shifts performed automatically. It is worth mentioning that the mechanical algorithm implemented in this machine can optimize the number of rotor turns, deciding whether to go forward or backwards so that the number of turns is minimized.

The operator can help minimizing the machine's effort. For instance, if the operator enters 333 x 999 =, the machine stores 333, then spins the rotor containing 999 three times at each of the three positions, so nine turns are required. If the operator enters 999 x 333, then 999 is stored, and with 333 in the main rotor, the machine performs one negative turn, then shifts left three times, then does one positive turn, and completes the task with only three spins.

Division is also fully automatic: after the dividend is input and added to the left of the accumulator, the input register is cleared automatically and the divisor can be keyed in and also shifted to the left. Then the division key starts up a mechanical algorithm by which subtractions and carriage moves to the right go on automatically until the remainder is zero or the precision limit is reached.

Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!

1951 FACIT ESA-0 s/n 327930

More about this machine

The evolution of FACIT calculators

Video: a demonstration of the FACIT ESA-0 features and use modes