The distribution of the ratio of the spiral field line length to the apparent path length obtained from VDA for the 1996–2016 events (161 in total). This quantity represents an estimate of the effective value of μ of the first-arriving particles. The left-hand bar in each speed bin represents the solar cycle 23 (1996–2008) events, the middle bar the solar cycle 24 (2009–2016) events and the right-hand bar all events during 1996–2016. The error bars denote the statistical error, only, and the numbers on the abscissa denote the lower limit of the μ bin. The last bin includes all the events for which L/s ≥ 1.