Fine tuning the Lego spectrometer more.
Using a maglite as the source eliminates the need for a separate collimating lens.
I also switched away from the very flaky variable slit made of a sliding brick that wouldn't stay in place if you looked at it wrong.
After some failed experiments with aluminum foil, I discovered that the round tree trunk Duplo brick was a tiny bit smaller than a nominal square 2x2 brick. When placed next to a square brick and locked in place with a plate on top you get a very consistent, repeatable slit that I'd ballpark as somewhere around 200 ΞΌm.