Train Tablet apparatus., Bernard Spragg Photo

The train-tablet system is operated to implement a train-spacing system designed to prevent more than one train occupying a single line section between any two tablet-stations at one and the same time. When the line is not occupied ( "Line Closed" ) their operation may permit the admittance of a train from one or other end of the tablet section. This is accomplished by requiring the driver of each train to carry an appropriate tablet, a hard-wood disc familiarly know as the biscuit. The biscuits not in active use are naturally locked up within the tablet instruments. The Tablets are severely rationed, not more than one can be extracted from the relevant cupboard at any one time. Control of the cupboards is remote...The unlocking of the instrument at the approach end of the section involves complementary action by the tablet porter at the terminal end, the one to which the given train is travelling, the withdrawal of the tablet leaves locked the instrument from which it is taken. It cannot be unlocked again for the obtaining of a successive tablet until the operator at the far station inserts into his own machine the tablet that has been carried along the entire section. It is however possible for a tablet to be replaced into either machine.