While a Neal's Ball Token Instrument may have been provided in the office,this is not a Token Instrument in the picture.This is a Key Interlocking system wherein the keys in their respective locks are used to unlock various signals and points.For...

While a Neal's Ball Token Instrument may have been provided in the office,this is not a Token Instrument in the picture.This is a Key Interlocking system wherein the keys in their respective locks are used to unlock various signals and points.For example,if the Home signal of Line No.1 is to be taken Off then the key for the same would be removed from the lock and given to a pointsman who would take the key to the signal post and unlock the signal and lower it.Once the signal is lowered,the key cannot be removed till the signal is again at On.Once the train has passed,the signal is normalised and the key removed and taken back to the SM.This is a very rudimentary system of interlocking and also time-consuming and is used only on lines with light traffic.