Minecraft wiki entry for Telegraph, associated text: Redstone repeaters, in their simplest form, can be used like the redstone torch receiver. However, they cannot be sent pulses as quickly or be mounted on walls, making them much more useful when placed in lines of two or more. This allows the receiving party to view a larger portion of the message as it is received, or, if the line is long enough, the entire message. The speed at which each pulse is displayed and lost can be adjusted by right-clicking each redstone repeater. This will increase or decrease the delay on each repeater before it passes on the signal. Such a system can be looped, so that the message is repeated to the receiving party indefinitely (note that looping a received message requires an erasing device and a message no longer than the receiver can display at one time).