Mardia (1967: J. Roy. Stat. Soc., Ser. B, 29: 320-342), and Batschelet (1972: Pages
61-91, In Animal Orientation and Navigation, NASA SP-262). The procedure for
the Ties Averaged case (Method 4) is described in Robson (1968: Biometrics
Unit, Cornell Univ. BU-258-M).