The counter register or "upper dial" is in two parts. The register itself is mounted in the carriage at the top right-hand end, while the operating mechanism is mounted separately on an oscillating bar at the rear of the machine. The operating bar is driven from the main clutch through another reversing mechanism and a pair of eccentric shafts.
The counter operating bar.
The counter operating bar is mounted between the main frame plates at the top rear of the machine.
It carries a set of ten cascaded spring-loaded fingers which engage with the transfer gears at the rear of the carriage register.
The counter drive mechanism.
This view shows the operating bar and the register gears from the rear of the machine.
The counter operating bar pivots on sliding links at each end, and is driven by the pin and arm near the bottom left. The fingers follow a roughly triangular path during every addition cycle, starting and ending at a point aligned with the tips of the gear teeth. The operating fingers first move downwards and forwards to engage below the tooth, then up to advance the gear and register, then back and down to the starting position. The vertical motion ceases before the fingers disengage, so that there is no possibility of overrun. A light detent holds the numeral wheel in position after the finger retracts. The oscillating motion is completed in 60mS, equivalent to 17 operations per second.
The first finger always engages with the register dial in the units column. The others are controlled by the rollers and notches in the gear flanges (and the cascaded connecting links) so that they only operate when a carry is required.
The operating bar drive mechanism.
The operating bar is driven at both ends by a set of eccentric shafts and links. This front view shows the arrangement at the left-hand end.
The rectangular drive bar A from the right-hand end rotates eccentric B, which is offset from its pivot in the frame plate. The lower end of link C moves in a circular path, which is converted by a curved slot at the fixed pivot D into a roughly triangular path at pin E. The counter bar slides and tilts on the (adjustable) pin F.
The operating bar is returned positively to its home position by a flattened cam and detent mechanism behind the spring-loaded lever G. The detent is released when lever G is pressed downwards as the carriage goes into the dip.
Also visible on the left of this view, but unrelated to the counter mechanism, are the carriage support bearing H, the shift terminating lever I operated by the tabulator fingers, the carriage dip arm J which pulls the main register down into engagement with the actuator, and the carriage centraliser K which rises between the main register frame plates at the start of the setting cycle.
The counter reversing gear.
This view shows the alignment of the reversing gears and idlers at the top rear of the control unit.
The counter mechanism is driven from the leftmost gear on the rear shaft. The other two gears on this shaft are rotated in opposite directions by the double idler (centre) and the reversing idler (under the inner left-hand gear) whenever the main clutch rotates. An internal sliding pin engages with the slot in the hub of one or other of the contra-rotating gears, transfering the drive to the internal shaft and thence to the leftmost output gear.
The sliding pin is operated manually or automatically by the shaped arm attached to the right-hand side plate. The register can be set to count either forward or back (for complements) by a thumb tab at the right-hand side of the keyboard. The linkage allows the chosen direction to be reversed automatically if necessary during division.
The counter clearing cams.
Rotating the counter clearing shaft through about 30° lifts the numeral wheel detents and pulls the roller arms downwards. The rollers act on the cardiod-shaped cams attached to the numeral wheels, driving them back to their zero positions. Numerals 0 to 5 rotate backwards towards zero, while 6 to 9 rotate forwards.