http://www.scribd.com/doc/228831637/Optimal-Tip-to-Tip-Efficiency

ukazka: It is physically unreasonable to allow jerk actions on three or more shafts with asingle hand — it is unclear how audience members could be arranged to performsuch a feat. However, there is considerable photographic evidence to suggestthat two shafts per hand is not only feasible, but efficient. We refer to this asa
double jerk
. There are primarily two ways in which a double jerk may beperformed (Fig. 2).1. Tip-to-tip (series jerking): two individuals stand facing one another, withtheir members touching tip-to-tip. A single hand moves across both shafts,treating them as one extra-long shaft.2. Shaft-to-shaft (parallel jerking): Two individuals stand facing one another,with their members against one another lengthwise. A single hand wrapsaround both shafts, treating them as one extra-thick shaft.We assume in the double jerk scenario that jerking must continue until
both
members have exceeded their gratification threshold.