Anita Mk 8 Calculator




			Early Anita Desktop Calculators Anita Mk 8



	Anita Mk 8 The Anita Mk 8, made by the Bell Punch Co. of Uxbridge, England, was launched in October 1961. Together with the concurrently introduced Anita Mk VII, for the continental European market, it was the world's first electronic desktop calculator. It was sold mainly in the rest of the world outside of continental Europe, and was announced at the Business Efficiency Exhibition, in London, in October 1961, but orders for it were not taken by the British distributor, Sumlock Comptometer Ltd., until January 1st 1962. This model and the Mk VII were the only electronic desktop calculators in the world for over two years, and many thousands were sold. Like the Mk VII it has a full keyboard and uses cold-cathode tube technology. Development of the Anita calculators was started in 1956 under Norbert Kitz (a.k.a. Norman Kitz), who had worked on the pilot version of the ACE (Automatic Computing Engine) computer project in the mid 1940s. The name ANITA, stands variously for "A New Inspiration To Arithmetic" and "A New Inspiration To Accounting". This became the family name for all the Bell Punch electronic models. Display - 12-digits Numerical indicator tubes (similar to "Nixie" tubes). Electronics - One Dekatron decade counter tube of type Hivac GS10D. About 180 cold-cathode tubes of types Mullard Z700U and Hivac XC31. Selenium rectifiers. 10 vacuum tubes (thermionic valves) of type ECC81. 1 transistor of type Ferranti ZT42. A pulse rate of 4 KHz is used by the electronics. This may appear to be very slow today, but it was very fast compared with the mechanical calculators available then, and is acceptable for calculations with the standard four functions. Size - 376 x 450 x 255 mm (14.75" x 17.75" x 10"), 13.9 Kg (30.5 lbs). The photographs show the machine with model/serial number C/8/009067/A. Cost in 1964 was £355 Sterling [about $1000]. Manufactured by the Bell Punch Company, Uxbridge, England. The manufacturer had previously specialised in full-keyboard, "Comptometer"-type, mechanical calculators. The early Anitas used similar full-keyboards and worked in a similar way to a Comptometer since just pressing one of the number keys of the main keyboard immediately added that number to the total being displayed - it was not necessary to press any = key. Addition is very fast since all the fingers can be used to press keys in different columns simultaneously. An article in the journal New Scientist in 1975 stated "The Anita machine was built under licence by numerous foreign firms, including Olympia in the United States and Sharp in Japan". If you can confirm that other companies did build these machines please get in touch with me. *If you have information about the development of Anita calculators, or know of somebody who worked there, please* *get in touch with me*.



	Advertisment for the Anita Mk 8, June 1964.

The keyboard of the Anita resembles that of the mechanical Comptometer, with the keys 1 to 9 in each decade.

For addition, the "+" key at lower left is engaged and numbers are entered on the main keyboard, directly in the appopriate decade column. Addition is instantaneous and the sum is produced as each key is pressed.

Subtraction works similarly after the "-" key is engaged.

The position of the decimal point is set by pressing one of the row of small buttons below the main keyboard.

For multiplication or division, the appropriate key at bottom left is engaged, then the first number is entered on the main keyboard. The second number is entered in the column of keys on the right with the decimal point entered in the correct position using the Mutiplier Decimal Point key.

This type of keyboard was to last into the next version, the Mk 9 which allowed chain multiplication, but thereafter a standard 10-key keyboard was used.

The 'U' shape to the left of the keyboard is a slide-in holder for a card with decimal conversions, especially for converting the old British Sterling currency to its decimal equivalent.

The rear legs of the Anita are extendable so that the whole machine can be tilted forward to place the keyboard at a more ergonomic angle.

Most of the case of the Anita is plastic, with the sides and the bottom being one large moulding.

With the display cover removed the 12 "Nixie"-type numerical display tubes are revealed. Each is mounted on the edge of a counter/display board and is lacquered red to give better visibility to the displayed number.
At the bottom of the display tubes and between them are neon lamps which are used to produce the decimal point in the display. This was a common feature of Anita calculators, and some others, into the early 1970s.


	Looking down from the rear with the keyboard hinged forwards, showing that the neon tubes for the decimal point (mentioned above) are actually attached to the keyboard. In the foreground is the power supply section.

The Electronics.

The electronics of the Anita Mk 8 can be grouped into four sections:

Keyboard decoding - circuit board on the base, under the keyboard.
Calculating logic - circuit board on the base, in the centre.
Counter/display boards - fourteen of these stand vertically towards the rear, with the middle twelve each carrying a numerical display tube. These plug into the Calculating-logic board.
Power supply - two circuit boards at the rear.


	Looking down from the right side showing the keyboard decoding board on the left, which has the Dekatron counter tube at the top. The logic boards are right of centre, and the counter/display boards stand vertically on the far right.

A closer view of the logic boards during operation - DANGER, HIGH VOLTAGES.

The horizontal main board, underneath, carries three vertical daughter boards. The tubes on the daughter boards are cold-cathode switching tubes and the black blocks are selenium rectifier diodes.

When a cold-cathode tube is switched to the ON state it glows orange like a neon lamp, as can be seen in 5 of the tubes on the daughter boards. When the machine calculates the tubes flicker and a different pattern of illuminated switching tubes results.


	Detail of the keyboard decoder board showing the GS10D "Dekatron" decade counter tube, with the small vacuum tube (thermionic valve) to its right, which is part of a blocking oscillator circuit providing driving pulses at a rate of 4000 per second.


	The GS10D "Dekatron" decade counter tube. The wires can be seen leading up to the assembly which contains the circular arrangement of electrodes, which is just below the dark area near the top.


	One of the ECC81 double-triode vacuum tubes (thermionic valves), with a 9-pin base.

The 13-pin base fits into a 12-pin socket, and an extra flying lead with a single socket is used which attaches to the anode centre pin.

Looking down on the top of the Dekatron.

In the centre is the metal circular disk of the anode. Around it is a circular array of thirty vertical electrodes made up of ten cathodes, ten "First Guides", and ten "Second Guides".

Note that there is a full circle of electrodes, but the distortion through the glass tube has made those at the bottom of the photograph disappear. The red mark is a blob of red paint on the top of the tube.


	Looking down on the top of the Dekatron during operation. There is a mauve glow around the electrodes as the discharge is passed from one electrode to the next around the assembly.


	For more information about the operation of the Dekatron, and about vacuum tubes, and cold-cathode tubes see the Technology Explained Section.

One of the 12 counter/display boards with the Nixie-type display tube mounted on the edge. The board holds ten XC-31 cold-cathode switching tubes and 5 black selenium rectifier diode blocks in a ring-counter circuit.

Each switching tube is connected to a number in the display tube, and only one switching tube is turned on at any time. When the board receives a pulse, the next switching tube in the ring counter is turned on and the next number in the display tube is illuminated. If the digit "9" is illuminated and another pulse arrives then the count wraps round the ring so "0" is illuminated and a carry pulse is directed to the adjacent board dealing with the next decade.

The ring-counter circuit can count down as well as up.

Each display board stands vertically and plugs into the main logic board.


	A small section of one of the display/counter boards, showing three Hivac XC31 cold-cathode switching tubes and a selenium rectifier.



	Opening the rear of the machine is very much like opening the case of an old radio, with vacuum tubes (thermionic valves), a multi-tap transformer, high-voltage capacitors, and high wattage resistors. The power supply board is mounted vertically. Below it are 8 vacuum tubes on the rear edge of the calculator logic board, where they are underneath the ventilation slots in the casing, so the heat from them can be disipated.


	Three of the vacuum tubes (thermionic valves) on the rear edge of the calculator logic board and the only transistor in the whole machine!


	As well as being advanced electronically, the Anita was also advanced in its construction. The following is an extract from the journal "Engineering" for March 1962:

"Intricate Moulding in ABS Plastic
A moulded plastics casing shown here is described by the makers, GEC (Engineering) Limited, Erith, as being particularly complex. This component forms the casing of the new Anita electronic desk calculator being marketed in the United Kingdom by Sumlock-Comptometer Limited.
The casing is of fabricated construction comprising 13 moulded items varying in weight from 0.13 to 50 oz. It is made of Cycolac T, an ABS plastic. This is said to have been chosen because of its strength and good surface finish.
The Moulded Plastics Division of GEC comment that because of the intricate nature of the design, several new techniques were evolved. One of the problems was the variation in thickness particularly at the points where bosses and fixing brackets were required. This was largely overcome, they add, by casting these bosses and brackets as separate items and then dovetailing and cementing them into position on the main component afterwards."

If you have information about the development of Anita calculators, or know of somebody who worked there, please get in touch with me.

The Anita Models Mk VII and Mk 8 was the only electronic desktop calculator for over 2 years, until 1964 when the transistorised Friden 130, IME 84, and Sharp Compet CS10A were introduced. In this time several tens of thousands of Anitas were sold world-wide.

Grateful thanks to Ken Buckles for the opportunity to acquire this machine.