'Electric Slide Instrument'

There is an interesting device known as an 'Electric Slide Instrument' in the Indoor ASM's office, carrying a number of levers on it corresponding to the running lines at the station. If a Station Master decides that a train is to be received on line No. 5, say, he will pull at lever No. 5 on the instrument and lock it in place. This action electrically releases the appropriate signal and point levers in the block cabin thereby eradicating any possibility of the cabin leverman pulling the wrong levers. When an ASM joins his shift of duty he can often make out which lines are occupied by a mere look at the Slide Instrument in his office -- levers that are withdrawn carry a locking collar with 'BLOCK' painted on it in red letters and refer to tracks which are occupied, the other remaining lines being vacant.