Issue I407 [80,resolved] Custom distributions in FLY2. As of 8.0.4-TEST2, a custom distribution can be incorporated as folllows in a FLY2 file. The distribution is defined by a function that returns a random number. function my_dist() return simion.rand() ^ 2 end particles { standard_beam { n = 100, ... ke = distribution(my_dist) } } Feature is undocumented in SIMION 8.0.2 manual. FLY2 files with custom distributions cannot be fully saved from the SIMION GUI. Edit with a text editor instead. Discussed further in http://www.simion.com/discuss/viewtopic?p=1628 Resolved in 8.0.4-TEST2