I might be wrong, but you might need need (at least) a 23x23 LED matrix to have a white border around the outside to give it the contrast needed (the "quiet zone", since QR data is black).
For those unaware, misjudging a dose of rapid-acting insulin by even a few units can prove fatal. Can’t fathom expecting a quarter of a unit and getting 100x the amount.
Perplex City was great, thanks so much for all you did on it! Fondly remember the community that built up around solving these. I lucked in to being the first to solve one of the silvers (Differently Lethal), and remember all the efforts to solve this one back in the day.