More after the image.
This photo is of interest as it was taken with the adder already installed at White City Stadium and shows the motors installed underneath the surface of the mounting table. The drive motors are not shown on the adders photographed in the factory. It is also of interest as differently constructed motors have specific characteristics and the annotation mentions the automatic speed regulation of the series wound D.C. motor. The speed regulator if required mentioned in the annotation, refers to the handle and lever that moves in an arc, that looks like a tram speed controller, under the tabletop, on the left of the right hand motor.
Of further interest is the note, that mentions certain shafts being sped up. This is mentioned elsewhere in the Photo Gallery however here it adds the reason for it, that being very busy groups on some shafts.
These groups refer to the way the ticket issuing machines are connected to the adders. TIMs (Ticket Issuing Machines) are associated with a particular solenoid that activates an escapement mechanism in the adding shafts. These groups are time division multiplexed onto the solenoid by an electromechanical device called a scanner or distributor. The reference to busy groups means that machines attached to the solenoids in an adding shaft are more busy than the machines in other groups. This principle still applies today as some areas of the racetrack always have more betting activity than others. The betting shafts are at the back of this adder and consequently are obscured from view. It is possible to glimpse one adding shaft on the right hand side and at the rear of this adder. There are mounting bars that run along the top of each of the ten adding units. It can be seen in the right hand adding unit running from the front towards the rear, about two thirds of the depth of the adder. A second mounting bar then runs at a lower level than the first the final one third to the back of the adder. Below this lower bar is the adding shaft for this adding unit, with its escapement wheels and epicyclic gears and solenoids that are activated by impulses from the TIMs resulting in the release of the associated escapement mechanisms to allow adding shaft rotation to record the transactions. This visible adding shaft is one of ten along the back of this adder.
Now to the sped up shafts. The busy groups result in the associated adding unit having the storage screw move quickly. The storage screw is a mechanical form of memory and stores transactions that are recorded as rapidly accelerating angular motion. The heavier, slower to accelerate equipment need time to accelerate and during this period the transactions need to be stored. The storage screw can be seen as a tubular device that runs from the adding shaft at the back of the adder to the front of the adder and underneath the higher mounting bar previously mentioned. These storage screws are described in the text associated with other images in the Photo Gallery. The reading of the storage screw must be sped up on the busy groups to ensure the storage screw does not reach its storage limit otherwise transactions will be lost. In electronics this would be considered an overrun error. I presume that all storage screw shafts are not configured to run at flank speed as the greater the velocity, the greater the stresses the equipment is subjected to. I had an epiphany regarding a similar comment about some shafts being sped up in the Brough Park section of the Photo Gallery. The result is that I now know it is easy to see which shafts are sped up. In this adder it is the shaft in the third and ninth adding units counting from the left. This is easy to see. The cogs mounted on the side of the table are the main drive cogs and the cogs that mesh with them provide the drive for their respective storage screws and adding shafts. As can be seen the third and the ninth pairs of cogs have a larger drive cog and a smaller driven cog than the others, resulting in higher angular velocity of the shafts associated with them.