Error (Flag Semaphore)
A semaphore procedural signal telling the receiver that the preceding character or group was sent incorrectly.
The sender makes the recognised error signal, then repeats or corrects the affected part of the message according to the signalling procedure in use. It should not be confused with simply waving both flags without an agreed meaning.
Clear pacing and acknowledgement reduce the chance that the correction itself will be mistaken for message content.

