The rotor is assembled one disc at a time, starting from disc 1 at the right-hand end. The pins and detent pawl are loaded onto the first disc, the setting ring is carefully fitted into place, and the next disc is added to hold it all together.

The discs have cast-in numbers, and the setting rings are stamped with the numbers of the matching discs. When all the discs are in place, the aligning rod is inserted and the assembly is secured with the threaded clamps at the left-hand end.

The 10mm hole in the carriage channel makes a convenient stand for the rotor during assembly.

The register clearing mechanisms are assembled first, then the numeral wheels and interlock cams are fitted onto their shafts.

The detent springs and balls are fitted into the wells at the front of the carriage. The detent levers are installed one at a time as their retaining rod is fed in from the side. The rod is secured by a clamping screw and washer to the right of the central pillar.

The registers are then fitted into position on the carriage frame, and secured with the links at either end and a screwed retainer in the centre.

The carry sense levers are assembled onto their shafts at the rear of the carriage, along with two fixed supports for the star wheel shaft.

Note that the carry lever on digit 13 is different. It has no detent, but has a small tail extending rearwards to operate the division bell in the base of the machine.

The star wheels for the counter register are installed as the shaft is fed in from the right (in this view).

The bracket around the central pillar is hinged from the star-wheel shaft, and is raised by cams on the register shafts during a clearing operation. It engages with an assembly in the base of the machine to provide the carriage-to-rotor interlock.

The brackets at either end of the back-transfer idler assembly are positioned over the star wheel shaft and engaged with the forked arm at the rear of the operating lever. The assembly is shown here in the raised position.

The accumulator star wheels are installed one at a time between the carry sense levers as their shaft is fed in from the right.

It may be necessary to make some lateral adjustments to the star wheel support brackets to ensure that all of the star wheels and carry levers can move freely.

With the carriage laid on its back, the carry sense lever detent pins and their tiny coil springs are installed from underneath and secured with the cover plate and three screws.

The detent mechanism should not be installed until all other adjustments to the carriage have been completed. The spring-loaded pins may be lost if the star wheel shaft is not in place to limit the fore-and-aft travel of the carry levers.

The drive gear, non-return pawl, and winding handle are assembled onto the top shaft and the handle is secured with a tapered pin. The handle interlock shaft and plate are fitted to the lower bushing and engaged with the return spring and the sliding comb on the back plate.

The counter register drive gear is attached to the left-hand side plate, but the rotor bearings are not installed yet.

The assembly on the floor of the base unit contains the division bell and the carriage-to-rotor interlock. Both mechanisms are coupled to the moving carriage by levers which slide along the horizontal surfaces.

The carriage positioning mechanism is fitted into the cut-out at the front left. Push-buttons on the two vertical links move the carriage one step at a time in either direction. The metal tab extending forward at the base of the unit unlocks the carriage so that it can be positioned quickly by hand. The upper forward-facing tab on the shift mechanism is not related to the carriage, but serves to engage the rotor clearing mechanism. This control was relocated on the later models to allow one-handed rotor clearing.

The rotor is installed before its bearings. The winding handle should be locked, and the rotor should be in its home position with the setting handles one position rearward of top. The right-hand end of the rotor shaft is inserted into the bearing opening, and the rotor locking ring is engaged with the grooved pin on the handle interlock plate. The left-hand end is then lowered down into its opening through the channel cut into the end plate.

Before finally installing the rotor bearings, it is necessary to:

• check the alignment and operation of the rotor non-return mechanism (on the inside of the right-hand side plate).
• check that the disc at the right-hand end of the rotor locking bar is properly engaged with the grooved pin on the handle interlock plate.
• align the drive gears so that the setting levers agree with the markings on the top cover.
• align the counter drive gear so that its operating finger passes cleanly through the cut-away in the rotor shaft.

The rotor is then positioned laterally to align with the carriage star wheels by fitting shim washers at the right-hand end. The left-hand bearing has a heavy cover plate on the outside, with an adjusting screw to eliminate any free movement.

After fitting the covers (27 screws!) and installing the carriage, the Original-Odhner is ready for another 50 years of service.