Early Anita Desktop Calculators
ANITA Mk 12 with Square Root

Anita Mk12 with Square Root

ANITA Mk 12 with Square Root

This very unusual model is an ANITA Mk 12 calculator which has been modified by adding the 'Square Root' function.  Grateful thanks to Gerard Timmerman for generously providing the photographs and information about this extraordinary machine which he has discovered.  If you can provide any information about its development please get in touch.

Display: 12-digits using 'Nixie'-type tubes.

Function: 4-function, square root.

Technology: Dektatron counter tube, cold cathode tubes, vacuum tubes, discrete transistors and other components.

Serial number of this machine: MK 12/72633/K/2 (it is not known whether this code is significant to the square root modification to this machine).

The photographs here can be compared with the standard ANITA Mk 12, which was the first ANITA with the now standard 10-key keyboard.  The ANITA Mk 12 was introduced in 1966, actually before the Mk 11.

The Lamson Industries (the parent company) annual report for 1967[1] mentions the Mk 12:
"Several of the research achievements of 1966 are illustrated in the report.  Foremost was the introduction of Anita Mark 12, a simplified keyboard electronic calculator designed in the first instance for the continental market, and now coming into production."
This suggests that the 10-key machine was favoured in continental Europe but the full-keyboard machines (the Mk 8 and Mk 9) were more popular in Britain.

Anita Mk12 Square Root with cover removed

Removing the cover reveals a display and keyboard similar to the standard ANITA Mk 12 except for the addition of the 'Square Root' key at the top centre of the keypad.

Inside Anita Mk12 Square Root

Here the keyboard has been hinged up on the right and the display boards have been hinged up on the left.  Note side view of the Hivac brand GS10D Dekatron tube towards the left of the bottom of the photograph.

Of especial note is the light-coloured circuit board partially visible at extreme bottom left with orange coloured cables leading toward it.  This is an extra board that has been added to the standard machine, see photographs below.


The rear of the added board shows that it is 'Veroboard' strip board, commonly used at the time for prototyping.


The front of the Veroboard shows discrete components, including transistors, diodes, resistors and capacitors, neatly mounted.


Close-up of the Veroboard to highlight how diodes are mounted using overhead conductor wires to form a matrix.


Another small piece of Veroboard holding a couple of transistors, together with a few diodes and resistors.

Anita Mk12 Sq Rt display board

Most of the rest of the electronics of this machine appear to be similar to that of the standard ANITA Mk 12.  Here one of the display boards has been removed from the calculator and shows one of the 'Nixie'-type display tubes on the right which is driven by the transistors along the bottom.

Anita Mk12 Sq Rt power supply

The power supply circuitry at the rear of this machine appears to be standard for an ANITA Mk 12.  At lower centre, just above the three pins of the AC plug are a pair of  ECC81 (12AT7) double-triode vacuum tubes.

All of the photographs of the ANITA Mk 12 with Square Root on this page are kindly provided by Gerard Timmerman.

This machine with its extra key for square root and the Veroboard with the extra circuitry is a mystery.
Gerard surmises: "The [extra] boards appear to be a prototype but they show a very well designed layout and are completely integrated in the wiring and assembly of the machine, so I am convinced it is done by Sumlock during production, and not an add on of later date.   The diode matrix probably encodes a sequence of operations that it repeatedly executed for the chosen algorithm.  The keyboard is not something that anybody would have been able to add a key to, but the actual root key is a different shape than the other keys, almost as if they bought the key from another manufacturer.
Considering the huge expense in 1967 to get such a machine I can't think that anyone would privately reverse engineer and fundamentally modify one with a SquareRoot function then, and a few years later you had Sqrt on pocket calculators, so it would not have been done in the early 70's by a second owner.  The machine was used by a company specialized in materials engineering, so I think they would have had the budget for a special edition and the need for square root, unlike financial people with no use for that function."

If you can provide any information about this mysterious machine and its development please get in touch.

The square root function had been provided in electronic calculators some years before, such as in the Friden EC-132 of 1965.  The first ANITA calculators with the square root function that were commercially marketed were the ANITA 1020 and the ANITA 1021,  launched in 1970.



  1. The Times, April 6, 1967.

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Text & photographs copyright © 2002 - 2023 Nigel Tout, except where noted otherwise.