Issue I362 [80,example,hs1collisionmodel,high,resolved] HS1 collision model did not accurately thermalize. Reported by davidl-200702. Description: It was reported that in the HS1 collision model, ions reach an equilibrium temperature somewhat lower than that of the gas temperature, when in fact the two should be equal (thermal equilibrium). For example, at 300K, mass 100 amu, pressure 0.1mbar, over 1ms, HS1 gives <KE> = 0.0259eV (~33% lower than gas KE = 0.0388eV), while a slightly different collision method gave 0.0385. HS1 also slightly underestimated dispersion. The problem was in the way impact_angle and gas velocity for the collision were handled. To be truly correct, one can first translate the velocity reference frame so that the gas particle is stationary. Fixing that gives a much a more correct ion temperature at equilibrium (e.g. ~300K). This is fixed in REV-4 of the Lua code in 8.0.2 (as well as REV-4 of the SL code on simion.com). Another unrelated change in REV-4 (of Lua version) is a slightly more accurate calculation of gas velocities at collisions. REV-3 assumed Maxwell-Boltzmann, which is a reasonable approximation, but it should actually deviate a bit from Maxwell-Boltzmann at low ion velocities. This issue is explained in the new notes.pdf. In practice, this probably doesn't makes much difference. Also, various other improvements were made to REV-4 (of Lua version), such as additional documentation, improved code structure, and enhanced statistical reporting. See the new notes.pdf in SIMION 8. Affects: 8.0.0-8.0.1 (and version 2 of the SL version on simion.com). Resolved in 8.0.2 (and version 4 of the SL version on simion.com).