This early Original-Odhner does not show a model number, but it appears to be a Model 11. The serial number 63128 suggests that it was made in about 1924. The machine is solidly built of cast iron and brass, and finished in glossy black lacquer. The mechanism is based on W.T.Odhner's design from 1890, and is typical of the entire Odhner production. Subsequent models added only minor variations in features and styling.

The rotor pinwheels are 54mm in diameter, with the setting levers spaced 7mm apart. There is a two-stage rotor clearing mechanism operated by the button at the lower left of the setting levers. As the button is pushed to the left it brings a shutter into the path of the levers, releases the setting lock on the rotor, and releases the rotor non-return pawl. As the winding handle is turned forward, the setting rings stop against the shutter and the rotor continues to turn under them, until they are all back at zero. The handle is then returned to the home position and the button released.

The carriage contains the counter and accumulator registers, which are cleared by a full turn of the wing nuts on either end. The accumulator carry mechanism extends only to 13 places. The counter register has a full tens-carry mechanism, with a manual reversing mechanism operated by the small +/- lever at the top left corner of the machine. The carriage can be moved one step in either direction by the two buttons at the front left of the machine, or continuously by pressing the small lever between the buttons. The buttons are attached to the base rather than the carriage, and operate vertically rather than horizontally, thus avoiding any tendency to move the whole machine.

In the early 1920s Odhner developed a range of pinwheel machines for calculations in Sterling currency. The machines were sold under the name "LUSID", from the usual notation "L.s.d" for pounds, shillings, and pence. Martin describes six LUSID models (A to H), each adapted to a specific type of Sterling-currency calculation.

The machine illustrated is generally similar to the Model 11 above, but has very different arrangements in the carriage registers. The accumulator has only ten places, the first three of which are replicated in reverse order towards the far right-hand end of the carriage. A sliding lever operates a pair of shutters to display different groups of digits. The counter register has two sets of six white dials, with three red dials between them. There are two counter drive pawls located three places apart, and interconnected with the carriage position by sliding cams.

The functions of this machine are not at all obvious. It appears to have been "investigated" many times in its 80-year history, and may not be in its original configuration.

Model 27 was the "standard" machine in the smaller 10 x 8 x 13 format, which formed the basis for most of the subsequent Odhner models.

The machine has a more angular base-plate, with handles instead of wing nuts for clearing the carriage registers. The rotor clearing button has been replicated in a push-button on the right-hand side of the machine, where it can be operated with the thumb as the handle is turned. Internally, the rotor pinwheels have changed from machined brass to a die-cast light alloy.

Model 27 has no tens-carry on the counter register, but is fitted with a back-transfer mechanism on the accumulator. After clearing the rotor, the mechanism is engaged by pressing the button to the right of the accumulator. Clearing the accumulator then transfers its contents back to the rotor. A small release lever is provided below the back-transfer button, in case it was pressed accidentally. The back-transfer mechanism became standard equipment on most subsequent models.

Model 22 has a setting check dial mounted above the setting levers, and a rotor clearing button only on the right-hand side. It has no back-transfer mechanism, and no tens-carry on the counter. The case is slightly taller than the Model 27, with a rear panel that slopes backwards to accommodate the check dial mechanism.

Model 29 has full tens-transfer on the counter register, with an automatic reversing mechanism replacing the manual +/- lever. If the first turn of the winding handle is negative (as in division), the mechanism will reverse the counter so that it shows positive turns rather than complements. The mechanism is reset when the counter is cleared.

The case has been extended slightly on the left to accommodate the reversing mechanism, but is otherwise identical to Model 27.

The Odhner model numbering was changed to a more consistent 100-series in 1950, with the colour scheme changing from black to dark blue. The only mechanical changes are the rectangular plastic buttons for the carriage shift controls, and a relocated rotor clearing button. This has been removed from the right of the machine and replaced with another small tab between the carriage shift buttons, making clearing a two-handed operation.

Model 125 is a wide-carriage machine with tens-carry on the counter and a check dial above the setting levers. The machine is finished in the new grey colour scheme from 1952.

There were many different models in the 100-series, with various combinations of wide carriage, back transfer, setting check dial, and tens transmission on the counter.

The Original-Odhner machines were re-styled in 1955, with a new all-alloy casing in various shades of grey. The "200" series was built from 1955 until the end of production in the early 1970s.

The attractive and functional styling of these machines is the work of Sigvard Bernadotte (of Bernadotte and Bjorn), a distinguished silversmith and industrial designer and a member of the Swedish royal family. The changes were mainly external, as the mechanism is basically identical to that of the Models 27 and 127 above.

A machine similar to this was the first and only mechanical calculator that I have ever used in earnest. I took Mathematical Methods at university in 1965, and spent many hours computing difference tables on a brand-new pin-wheel calculator.

Model 239 has a tens-carry mechanism on the counter register, and a check dial above the setting rings. The case is slightly longer and higher than the Model 227 in order to accommodate the check dial.

The Odhner model numbering was changed to a 1000-series in 1967, with the colour scheme changing to a very light grey and white. The mechanism of this Model 1049 is identical to Model 239.

The Odhner LX11C-5 is a motor-driven adding and listing machine for Sterling currency. The keypad has two additional keys for 10 and 11 pence, but there are no Farthings.

The two function keys on the right-hand side serve dual purposes. The Add key will add if there is an entry in the keyboard, or take a sub-total if nothing has been entered since the last operation. Subtract and Total are combined on the other key in a similar manner. There is a Repeat key next to the two function keys, with Non-add and Clear keys at the left-hand side. A key marked "WN" switches the machine from 10-column Sterling into 7-column decimal mode.

The Odhner E11C-2 is a basic motor-driven add-list machine for decimal currency. The machine has the Add and Subtract keys on opposite sides of the keypad. Two sliding buttons control the Repeat/Clear and Total/Subtotal functions.

The Odhner XX11C-9 is a large electrically-driven machine which includes a mechanism for semi-automatic multiplication.

The first factor is set on the keyboard in the normal manner. The multiplier is entered one digit at a time (starting with the least significant) on the red auxilliary keyboard at the far right-hand side. The multiplier keys are so small that a normal finger will press about three at a time, but the mechanism is designed so that only the highest key will take effect.

This machine performs "short-cut" multiplication for digits 6 to 9. For example, to multiply by 8 the machine subtracts twice then adds once in the next column, so that the operation is completed in three machine cycles instead of eight. When all digits have been processed the operator clears the keyboard and takes a total to print the result. The clearing function has been designed so that if the key is held down, the machine will make another cycle and take the total automatically.

The instruction booklet for this machine is dated 1965. It includes an illustration of a similar machine with a wide paper carriage, captioned as a "fully automatic bookkeeping machine with electronic line-finder".

The Odhner 1207 is a motor-driven machine for decimal currency, from around 1970. It is generally similar to the E11C-2 above, but has separate keys for Total, Sub-total, and Non-add on the right-hand side.