The Elettrosumma 14 is a basic but very substantial electrically-operated add-list machine from Olivetti's early post-war period.

The Summa 15 is a manually-operated "ten-key" machine with two additional keys for Sterling currency.

Operation is similar to a decimal machine, but with automatic restrictions on the values that can be entered in the pence (first, or rightmost) and ten-shilling (third) columns. Pressing the 10 or 11 keys enters the value and immediately locks the keyboard, so that the current column perforce becomes the rightmost. The third-last place is always the ten-shillings, and will only ever register 0 or 1, regardless of the key pressed. Entering values in the common format of (say) 37/6 will register only 17/6, instead of the expected £1/17/6. A small lever above the keyboard can be set to disable the three Sterling columns, so that the machine will operate in the normal decimal mode on the seven leftmost columns. The single-digit window to the left of the keyboard counts the number of cycles in each place when the machine is set for multiplication mode.

The Prima 20 is basic 10-key office adding machine with add, subtract, total, and sub-total. As a manually-operated machine it retains the joystick and most of the functions of the Summa 15 (above), but is less than half the weight. The mechanism sits in a pressed-metal base with a moulded plastic cover. The "missing" front foot is actually located about three inches towards the rear.

This 1960s machine operates in either Sterling or decimal currency, as selected by a small lever on the under side of the base.

An early Prima 20 for decimal currency. This machine was built in Italy, but others found in Australia have come from the Olivetti factories in Argentina and from assemblers in South Africa.

These machines were supplied as replacements for Sterling add-list machines during Australia's conversion to decimal currency in 1966. Most of them were retired in the early 1970s, after relatively little use, in favour of the new electronic calculators. They can still be found in large numbers, and are generally still in good working order.

A late-model Prima 20 for decimal currency, with square keytops and a white plastic bezel around the function joystick. The purple sheet-metal base has been replaced with a dark grey plastic tray.

Olivetti acquired a controlling interest in the Underwood company in 1959, and used the Underwood name primarily on machines intended for the American market. This Underwood 200 was sold in Australia by Stott & Underwood, a long-established firm of office equipment suppliers with obvious overseas connections. The internal mechanism is identical to the Olivetti Prima 20, except that the four-way joystick control has been replaced with two separate levers operating at right angles.

The Quanta 20 is a motorised version of the Prima add-list machine. The joystick has been retained for Total and Sub-total, but on a motor driven machine the other functions are more easily controlled from the keyboard.

The Quanta 20R is a "reduced" version of the Quanta 20, with only 8 places in the keyboard and 9 in the result and printing mechanism. It has square keys, a grey plastic base, and asymmetric feet, but is otherwise the same as the Quanta 20. This machine was built in the Olivetti factory in Argentina.

A larger 10-digit machine in a similar plastic casing, with all of the controls on the keyboard.

A 10-digit machine with a multiplication function, rather than just a "Repeat" key.

The Elettrosumma 22 is a large, heavy-duty add-list machine from the 1950s and 60s. It has 12 places in the keyboard and 13 in the result mechanism. The printing mechanism has another four hand-settable print wheels to the left of the numeric columns. It accommodates paper up to 100mm wide.

This Sterling-currency version has five additional pence keys (1/4, 1/2, 3/4, 10, and 11) located just above the main keypad.

An all-decimal version of the Elettrosumma 22 from 1966. The owner of this machine was obviously unhappy with the green-and-black colour scheme, and has had the covers professionally spray-painted in high-gloss enamel. That's one way to brighten up the office...

A 12-column version of the lightweight Elettrosumma machine, in a re-styled plastic casing.

The Olivetti Divisumma 24 (D24) is a large full-function printing calculator with fully automatic automatic multiplication and division.

The calculating mechanism was designed by engineer Natale Capellaro, and the exterior by the noted architect and industrial designer Marcello Nizzoli. The machine first appeared in 1948 as the manually-operated Divisumma 14, in a casing similar to the Elettrosumma 14 (above). The machine was extensively redesigned in 1956 to become the Divisumma 24, which continued in production in various forms well into the 1960s. An electronic Divisumma 18 appeared in 1973.

The D24 operates as an adding machine in the normal manner, with keys for add, subtract, total, and subtotal. To divide, the dividend is entered into the accumulator with the add key, and the divisor is set on the keyboard. When the division key is pressed the machine completes the calculation automatically and prints the quotient and the remainder.

Problems in multiplication are entered as written, eg "123 x 456 = ". The machine stores the first value, performs the calculation, and prints only the result. There are options for controlling the printing of totals and accumulated subtotals during repeated multiplications.

The Divisumma performs short-cut multiplication for numbers over 5. It takes 6 machine cycles to multiply 5 x 5, but only 3 cycles for 2 x 2 or 9 x 9.

The internal storage register which holds the first factor in a multiplication is directly accessible from the keyboard (via the M and IM keys), and can be used as a general-purpose memory register. Values can be entered directly or back-transferred from the accumulator, and can be returned to the accumulator or used in a subsequent multiplication.

The Multisumma 24 is essentially the same as the Divisumma 24, but without the automatic division.

Internal view (33kb).

This 24-series Elettrosumma is fitted with an automatic power-driven paper carriage for bookkeeping and accounting applications. The machine is larger and heavier than the previous models to provide stability for the rapidly-moving carriage. The extended rear feet are an integral part of the cast-iron baseplate, which is over 30mm thick in places. The painted covers are metal die-castings instead of plastic.

The basic calculating mechanism is common to all the members of the 24 series. The Elettrosumma omits the multiplication, division, and memory functions, but has an improved date-setting mechanism operated by the small red levers to the left of the main print wheels. The date can be printed on demand in the format 01 JAN 99.

The paper carriage accommodates rolls, sheets, and printed forms. The platen roller is divided about 75mm from the left-hand side, allowing forms to be changed without affecting the continuous tally roll.

A full-width cover at the rear of the machine provides access to the carriage programming mechanism. Cam plates are selected according to the functions required, and are inserted in the corresponding positions around the 55-place drum. The drum rotates in synchronism with the carriage movement, and controls the functions of the machine through an array of sensing levers at the left-hand side.

Carriage programming mechanism - rear view (29kb).

The Divisumma 26GT is a further development of the 24 series, with a number of changes and improvements to the mechanism. The angular casing and its bright orange trimmings are the work of the famous Italian designer Ettore Sottsass. Production of these machines continued into the 1970s.

Olivetti's traditional attention to industrial design continued well into the electronic era. This Divisumma 422 from the 1980s uses four different background colours to enhance the logical separation of the keyboard functions. Even the internal elastomeric key sheet. seen only by technicians, is an elegant blue colour instead of the usual black or grey. The small impact printer gives a particularly clear and well-formatted listing. The circuitry uses just one 64-pin chip (Hitachi HD614042S) and a handful of minor components to far surpass the capabilities of the mechanical calculators above.