Gents' slave dials could be found in many establishments from schools, to office blocks, palaces, factories, stations, airports and hospitals. The Gents' master clock and slave dial system could be installed anywhere to provide uniform time across a whole complex of separate rooms or buildings. All would be wired in series with the master clock. Here is just a very small selection of the many styles of slave dials available. Some slave movements were even housed in mantle clocks.
The service of providing the time, free of charge, was once much used in advertising and business promotion. Particularly before it became commonplace for the general public to own accurate watches. A time service required accuracy and reliability or the poor timekeeping would reflect badly on the business. The cost of installing a master clock and advertising dial on the façade must have been less expensive, and much less trouble, than a weight-driven turret clock movement. I knew of several shops in one town, in the UK, which all had their own master clock and prominent advertising dials. Perhaps they had a very persuasive, local salesman? Or they each copied each other?
Many different styles of advertising dials were made to hang outside business premises. Sometimes double sided or even three or four sided. Plain or highly ornamented to taste. Usually with slightly larger, double locking slave dial movements. Or designed to be driven by mechanical lead-off rods from a WT. Depending entirely on the size of the dials involved and whether exposed clock hands were desired.
I once had a smaller example of one of these iron dials but traded it in towards another master clock. The dial was really, quite remarkably heavy. Had it been a slave movement, rather than having a mains motor fitted, I would probably have kept it. Ah, the wisdom of hindsight.
I had a large double-sided station dial, as well, but it was far too large to be of much use to me. Again it was traded towards another master clock. The two slave movements inside looked about the same size as standard wall dials but had double locking. Which made hand setting extremely tedious.
Slave dial hand setting:
Normally one can just press the armature against the electromagnet core and whiz the hands round the dial by pushing on the large ratchet wheel. One quickly reaches almost to the time to which it is desired to set the hands. Then one releases the armature to relock the movement. Pressing repeatedly on the armature, against its return spring, will now bring the hands to exact time in half minute jumps.
Usually the master clock is still running and one should allow it to impulse before finally setting the hands to the exact time. Otherwise the dial will show a half minute fast and you will need to go right around the dial again. Hopefully remembering to stop slightly short of the real time. Though I usually insert a fingernail between the armature and electromagnet. Just to stop the movement impulsing for the next half minute.
Double locked slave dials may have a special lever to aid rapid advancing. Though usually one must resort to manual dexterity by holding the impulsing and locking detents clear of the ratchet wheel. The wheel can then be spun to show the correct time with one's third (or fourth) thumb.
An 18" slave dial with pressed steel case and flat glass. Large enough for an assembly hall, canteen, station, corridor or school gymnasium. The poor weather protection makes it obviously intended for indoor use. Plain baton hands are used here suggesting a later dial. Note the superb clarity of a dial meant to be read from a distance. The distortion in shape is due to the low camera viewpoint. Being indoors the glass reflects no distracting light.
I have taken advantage of another eBay auction to share some excellent images of a Gents "W1" turret clock, slave movement. Don't ask me about copyright. I have no idea where eBay auctions are concerned. It is not my intention to profit from sharing these images or information. One must hope that the seller sees such image borrowing as beneficial during the period of the auction. And won't care after the event.
The usual, back view showing the drive electromagnet, double locking and over-dimensioned components. All designed to handle the heavier loads of larger clock hands over a long period of service. Notice how compact the slave is and how easy it would be to fit into a small recess in a wall. Or behind any partition. See my "bell programmer" chapter for the use of a similar, oversize slave movement to provide motive power for a programmable, time switch.
Side view showing the hour pipe and minute arbor and motion work between the plates. Interestingly, Gents has gone the extra mile and provided a bronze minute shaft and brass hour pipe. Thus hoping to avoid potential corrosion problems. The movement was supposed to be used with the hands behind glass. However, breakage in an inaccessible situation might mean he clock being required to perform for a extended period in a less than weather-proof situation. Even though this was not the manufacturer's original intention it was guarded against from long experience.
The length of the hour pipe and minute shaft suggest it was designed to protrude through a wooden building rather than through a brick wall. The seller suggests a 3' dial capacity behind glass. Under the protection of a deep roof overhang or indoors it could manage with exposed hands provided (as always) that they are well counterbalanced. (to void the movement having to lift the heavy minute hands before the hour) Exposed hands subjected to the weather should probably be limited to less than half that dial diameter. Note the complete lack of any ferrous materials which might rust and shorten the life of the movement.
The side which would rest against the back of the dial or perhaps a partition wall. The seller suggests 24V DC minimum to achieve a brisk hand movement from the short, half minute impulse of the series clock circuit. As always, the freedom from regular rewinding made such movements attractive for inaccessible positions such as gable ends, chimneys, stables or barns. The limitation being that a glass dial cover was highly desirable to protect the hands from bad weather. The limited torque available might not cope well with ice, snow or gales. Here the WT would offer power aplenty but at much greater expense, bulk and complexity.
One serious problem with glazed dials with plane (flat) glass is the difficulty of reading the time through the highly reflective glass. Particularly out of doors where a cloudy sky can completely obscure the time by reflecting in the glass. I do not think glazed dials are particularly suitable for church towers or other raised situations. Where the sky is very likely to spoil the view of the clock hands during many, unfavourable sky conditions. I pass a rural house regularly which has a glazed dial raised high on the façade. It is extremely difficult (and usually impossible) to read the time under any lighting conditions. An overhang above a glazed dial will often help to reveal the hands more clearly by reflecting a dark surface instead of the bright sky.
A sheet copper cased 10" slave dial from 1937. One of a matching, signed pair with the same dates and consecutive numbering. The copper should really be polished and lacquered but I have never quite got around to it. The hands are typically Gents'.
An 8" dial with a convex Bakelite case and convex glass typical of office and classroom. I can still remember the long delay between the half minute clicks of the slave clock during the more boring lessons at school. Since I was usually so well behaved it was a once-only treat to watch the master clock and programmer in the headmaster's office while waiting for his return.
Dials were also made with seconds hands but these needed extra components in the master clock. No doubt the noise from these dials dial could be a problem in some circumstances. Gents provided silent movements as part of its range where any noise was a problem. Such as in radio, TV and music studios.
An impulse clock system would usually have trickle charged, backup batteries and happily continue running for the duration of the power cut. Synchronous mains dials can usually be recognised by a motor starting and hand setting rod or knob protruding from the bottom of the dial case. Though not always. So if you do find a dial for sale ensure it matches your needs by checking around the back. It should be obvious whether a standard, rectangular, Gents' Bakelite cover conceals a slave movement. Or a tin can is hiding a synchronous electric motor.