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Tyers No 6 single-line tablet instrument. This one was photographed, still in use, at Cromer Yard.
Thanks to John Hinson for kind permission to use this image from his Signal Box web site, where more information about Tyers and other signalling instrument is available.
Tyers single line instrument
Opened between 1881 and 1891, the MSWJ missed the early 'disc and crossbar' days of railway signalling. The last section, the Swindon-Cheltenham extension, was opened throughout in 1891, and this was controlled from the outset by Tyers single-line tablet instruments. It should be remembered that the doubling of the section northwards from Cirencester did not begin for some years.

The MSWJ had adopted these instruments for single-line control from 1890, when they had replaced staff -and-ticket working. Staff-and-ticket working is still approved today as safe system, but it lacks the flexibility required to operate a potentially busy through route. No driver may enter a single-line section unless he has possession of the staff, or unless he has been shown the staff and received a ticket as authority to proceed. All is well with this system while trains are running in their expected order, but any change in the schedule brings the possibility of disruption. If a train needs to enter one end of a section while the staff is at the other, it cannot proceed until the staff is fetched. .

The electric tablet system overcomes this difficulty. There is an instrument at either end of each single-line section, linked by telegraph wire. As long as there is no train on the line, a tablet may be withdrawn from either instrument and given to a driver as his authority to proceed. But, while a tablet is out, it is not possible to withdraw another one until it has been returned to one or other of the tablet instruments. .

Tyers instruments were pioneers in bringing the flexibility and safety of electrically-interlocked instruments to single-line train control. With them came the need for a new set of Regulations, and those issued by the MSWJ can be seen on other pages of this web site. They, themselves, are, of course, the successors of earlier Regulations, but they are also amongst the first generation to bear the title Regulations for Working Single Lines by Train Tablet. They make an interesting comparison with those issued by British Railways and its successors.

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