A validation technique that counts the directional swings in a putative impulse. A simple non-extended five-wave impulse contains exactly 5 swings; each level of extension adds 4 more, producing the valid series 5, 9, 13, 17, 21, 25, … (arithmetic with common difference 4). A count of 7, 11, or 15 indicates the impulse is either incomplete or mis-labelled.