Block Instruments used in Indian Railways

Last time we have discussed about the block working in Indian Railways, there I have mentioned about a term Block Instrument. So you may be confused about what the Block Instrument actually mean and what it does. A Block Instrument is the apparatus kept at a block station where station master use this to give line clear to or receive line clear from adjacent block station. It is basically a communication equipment between two block station used to implement absolute block working. They are avail...