Use a brim of 5 mm. I used the legs of a diode for hinge wire, smooth paperclips would work well too. Smooth the lip of your can so it makes a nice seal against the balloon. A small bit of double stick tape can be used to keep the little leg on the same spot of the balloon for repeatable results. The further you can send your laser spot the more sensitive the barometer will be! Adjust your laser so it is well balanced in the holder for best results. .4 mm print head used. Print each part separate for best results.