The helix of the antenna can twist in two possible directions: right-handed or left-handed, the former having the same form as that of a common corkscrew. The 4-helix array in the first illustration uses left-handed helices, while all other illustrations show right-handed helices. In an axial-mode helical antenna the direction of twist of the helix determines the polarisation of the emitted wave. Two mutually incompatible conventions are in use for describing waves with circular polarisation, so the relationship between the handedness (left or right) of a helical antenna, and the type of circularly-polarized radiation it emits is often described in ways that appear to be ambiguous. However, Kraus (the inventor of the helical antenna) states "The left-handed helix responds to left-circular polarisation, and the right handed helix to right-circular polarisation (IEEE definition)". The IEEE defines the sense of polarisation as "the sense of polarization, or handedness ... is called right handed (left handed) if the direction of rotation is clockwise (anti-clockwise) for an observer looking in the direction of propagation" Thus a right-handed helix radiates a wave which is right-handed, the electric field vector rotating clockwise looking in the direction of propagation.