1. Rev A — dev board on a breakout, sensors wired up, firmware proving the concept
2. Rev B — custom PCB in KiCad, enclosure modeled in Fusion 360, printed in PETG or machined from Delrin for cold tolerance
3. Rev C — production-intent board with the right certifications in mind (FCC, CE, and for pharma, often ATEX or IECEx if there's any risk of flammable refrigerant)