Thanks Robin, will do. After the E&I meet, because it’s easy to set away APT running short 6s exposures during the night when dark enough, I was able to time and fire the green 532nm LASER and move around various targets whilst I could hear APT finish exposure, start exposure…..etc, so managed to build up a few shots to work with. Some will be squiggled, other’s nice and clean dots. I should be able to measure the dispersion in pixels (or mm on screen) and see what we get. I have a suspicion that I’m going to get slightly different dispersion distances for n = +1 and n = -1, possibly because of the grating, being plastic, it’s not completely flat but is curving. Depending on where the dot occurs, if it’s on a part that’s more curved, relative to the opposite side of the zero order image, we might get discrepancies there. All nice experimentation. could make decent experiments for school projects.