The rotor consists primarily of ten die-cast pinwheels assembled side-by-side on a central shaft. The pressed-metal setting rings rotate in grooves between each pair of segments to raise or lower the pins. Three additional rotor segments to the left of the pinwheels extend the tens-carry across the full width of the accumulator register. A screwed bushing at the left-hand end clamps the segments tightly together to form a rigid assembly.

The rotor shaft is supported in plain brass bearings in the two end plates, and is driven 1:1 from the winding handle by a pair of plain steel gears.

The die-cast pin-wheels are 53mm in diameter and 7mm thick at the centre. The thickness of the wheel determines the horizontal spacing of the digits. The setting ring is inset 1.5mm into the top (or left-hand) face of the pin-wheel. A groove and cam are cast into the bottom face for the carry reset, leaving a rim only 3mm wide around the outside to hold the pins. The discs are mounted side-by-side on a 10mm keyed shaft, with a separate locating rod through the round hole to maintain alignment.

The nine retractable pins measure 1.5 x 1.7 x 10mm, and slide in the channels cast into the disc. Two pins are shown in side view. Note that the pins on each disc are not aligned horizontally across the rotor (see the previous view), but are staggered to operate at slightly different times, giving a smoother and less "clunky" feel.

The spring-loaded detent pawl holds the setting ring in definite positions as the numbers are entered. A locking bar through the rectangular slot clamps the pawl and ring when the rotor is in motion.

The cut-out in the outside of the disc (near the detent pawl) provides clearance for the back-transfer gears to engage with the setting ring.

The two extended pins on either side of the detent pawl are the carry operating fingers, which move vertically (in this view) on their pivots. Two compression springs are set into the disc under the short ends of these fingers. The pivot pins are staked into the die-cast disc and are not removable.

The carry fingers are arranged in sequence from discs 2 to 10 (actually, to 13) so that a ripple carry can propagate across the whole machine. There are two sets of carry fingers, arranged symmetrically on either side of the retractable pins, to provide for carries on both addition and subtraction.

Note that in order to reduce the number of castings, most rotor discs have two alternative locations for the carry fingers. This disc could be used for either position 2 or 10 (labelled near the top), depending on how it was assembled at the factory.

The setting ring performs six different functions:

• The handle at the top rotates the ring to set the pins manually.
• The ramped slot at the left raises or lowers the pins and holds them in position as the ring is rotated.
• The teeth on the inside of the ring engage with the spring-loaded detent pawl to provide a positive setting.
• The teeth on the outer right-hand side engage with register gears to rotate the setting ring during a back-transfer operation.
• The teeth on the outer left are used (on more elaborate models) to drive a numeral-wheel display of the rotor setting.
• The long tooth at the bottom of the ring is part of the rotor "quick clearing" mechanism.

There are five different setting rings, with the ramped slots in slightly different locations to suit the staggered arrangement of the pins. Each ring is stamped with the numbers of the two matching discs.

This view shows the notched locking bar partially withdrawn from the rotor.

The detent pawls align with the notches when the bar is fully inserted, allowing the setting rings to rotate. Withdrawing the bar by about 2mm blocks the movement of the detent pawls and locks the setting rings in position.

The locking bar is operated automatically from the winding handle, via a yoke over the disc at the right-hand end.

The rotor lock is operated by a shaft through the extended bushing below the winding handle. The tip of the shaft is visible in the centre of the vertical slot at the end of the bushing. The shaft is spring-loaded outwards, into the locked position.

The pin on the inside of the winding handle sits in the vertical slot when the machine is at rest. This pin is loaded to the left by a much stronger spring inside the handle.

When the machine is at rest, the handle spring pushes the locking shaft inwards, releasing the lock and allowing the setting rings to rotate. When the handle is pulled outwards to commence a turn, the locking shaft follows and locks the rotor.

This view shows the 223 component parts of the rotor (minus the locking bar), arranged in order.

At the top left are the counter drive gear and the rotor clamping components. Next comes an interlock disc, followed by the three extended-carry discs and the ten pinwheels. At the lower right are the quick-clear interlock disc, the drive gear, and the non-return gear.

The slotted and keyed mainshaft and the small aligning rod are at the bottom. The two zip-lock plastic bags contain the 90 pins and the 10 detent pawls and springs.