That’s a great piece of experimentation. It’s interesting to see what looks like a linear relationship. I wonder if this is a kinetic effect in the diode mechanism (Arrhenius equation etc)? compared to the transition in neodymium for the green light that Steve mentioned (maybe the transition in neodymium is not sensitive to temperature changes?). It’s all good because this discussion has led me to standardising on using the green LASER. In fact (out of curiosity) I may calibrate the blue and red LASERs using the green one as the primary standard. For meteor spectra surveys, it will be easy to make a green LASER calibration frame/s at the start or end of a batch of exposures [better at the start because of the dew formation later]. But I think once done and I have a value of the number of pixels the green LASER is dispersed in the first order diffraction, as long as the equipment stays the same, lens, focal length, grating, do you think the calibration will no longer be necessary ? Oh, I think I need to follow up with Robin’s comments on distance. I will need to do some exposures with various objects at different distances painted with the LASER. Robin, do you think it’s important to know the actual distances? A problem I have is, I don’t know the distances – they are just roof tops, aerials etc. Is there a way to work out their distances?